U.S. patent application number 10/329046 was filed with the patent office on 2004-01-08 for conductive lithium storage electrode.
This patent application is currently assigned to Massachusetts Institute of Technology. Invention is credited to Andersson, Anna M., Bloking, Jason T., Chiang, Yet-Ming, Chung, Sung-Yoon.
Application Number | 20040005265 10/329046 |
Document ID | / |
Family ID | 27407546 |
Filed Date | 2004-01-08 |
United States Patent
Application |
20040005265 |
Kind Code |
A1 |
Chiang, Yet-Ming ; et
al. |
January 8, 2004 |
Conductive lithium storage electrode
Abstract
A compound comprising a composition
A.sub.x(M'.sub.1-aM".sub.a).sub.y(XD.s- ub.4).sub.z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(DXD.sub.4).sub.z, or
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z, and have
values such that x, plus y(1-a) times a formal valence or valences
of M', plus ya times a formal valence or valence of M", is equal to
z times a formal valence of the XD.sub.4, X.sub.2D.sub.7, or
DXD.sub.4 group; or a compound comprising a composition
(A.sub.1-aM".sub.a).sub.xM'.sub.y(XD.su- b.4).sub.z,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z and have
values such that (1-a).sub.x plus the quantity ax times the formal
valence or valences of M" plus y times the formal valence or
valences of M' is equal to z times the formal valence of the
XD.sub.4, X.sub.2D.sub.7 or DXD.sub.4 group. In the compound, A is
at least one of an alkali metal and hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
molybdenum, and tungsten, M" any of a Group IIA, IIIA, IVA, VA,
VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at
least one of oxygen, nitrogen, carbon, or a halogen,
0.0001<a.ltoreq.0.1, and x, y, and z are greater than zero. The
compound can have a conductivity at 27.degree. C. of at least about
10.sup.-8 S/cm. The compound can be a doped lithium phosphate that
can intercalate lithium or hydrogen. The compound can be used in an
electrochemical device including electrodes and storage batteries
and can have a gravimetric capacity of at least about 80 mAh/g
while being charged/discharged at greater than about C rate of the
compound.
Inventors: |
Chiang, Yet-Ming;
(Framingham, MA) ; Chung, Sung-Yoon; (Seoul,
KR) ; Bloking, Jason T.; (Santa Clara, CA) ;
Andersson, Anna M.; (Uppsala, SE) |
Correspondence
Address: |
Timothy J. Oyer
Wolf, Greenfield & Sacks, P.C.
600 Atlantic Avenue
Boston
MA
02210
US
|
Assignee: |
Massachusetts Institute of
Technology
77 Massachusetts Avenue
Cambridge
MA
02139
|
Family ID: |
27407546 |
Appl. No.: |
10/329046 |
Filed: |
December 23, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
60343060 |
Dec 21, 2001 |
|
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60388721 |
Jun 14, 2002 |
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60412656 |
Sep 20, 2002 |
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Current U.S.
Class: |
423/306 ;
423/326; 429/231.5; 429/231.6; 429/231.95 |
Current CPC
Class: |
Y02E 60/10 20130101;
Y02C 20/40 20200801; Y02E 60/32 20130101; H01M 4/74 20130101; H01M
4/5825 20130101; H01M 4/523 20130101; H01M 4/70 20130101; H01M
4/382 20130101 |
Class at
Publication: |
423/306 ;
429/231.95; 429/231.6; 429/231.5; 423/326 |
International
Class: |
H01M 004/58 |
Claims
What is claimed is:
1. A compound comprising a composition
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X- D.sub.4).sub.z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(DXD.sub.4).sub.z, or
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z, having a
conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm,
wherein A is at least one of an alkali metal or hydrogen, M' is a
first-row transition metal, X is at least one of phosphorus,
sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and
tungsten, M" is any of a Group IIA, IIIA, IVA, VA, VIA, VIIA,
VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of
oxygen, nitrogen, carbon, or a halogen, 0.0001<a.ltoreq.0.1, and
x is equal to or greater than 0, y and z are greater than 0 and
have values such that x, plus y(1-a) times a formal valence or
valences of M', plus ya times a formal valence or valence of M", is
equal to z times a formal valence of the XD.sub.4, X.sub.2D.sub.7,
or DXD.sub.4 group.
2. A compound comprising a composition
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X- D.sub.4).sub.z,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, having a
conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm,
wherein A is at least one of an alkali metal or hydrogen, M' is a
first-row transition metal, X is at least one of phosphorus,
sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and
tungsten, M" any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA,
IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen,
nitrogen, carbon, or a halogen, 0.0001<a.ltoreq.0.1, and x, y,
and z are greater than zero and have values such that (1-a).sub.x
plus the quantity ax times the formal valence or valences of M"
plus y times the formal valence or valences of M' is equal to z
times the formal valence of the XD.sub.4, X.sub.2D.sub.7 or
DXD.sub.4 group.
3. A compound comprising a composition
(A.sub.b-aM".sub.a).sub.xM'.sub.y(X- D.sub.4).sub.z,
(A.sub.b-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.b-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, having a
conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm,
wherein A is at least one of an alkali metal or hydrogen, M' is a
first-row transition metal, X is at least one of phosphorus,
sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and
tungsten, M" any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA,
IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen,
nitrogen, carbon, or a halogen, 0.0001<a.ltoreq.0.1,
a.ltoreq.b.ltoreq.1, and x, y, and z are greater than zero and have
values such that (b-a).sub.x plus the quantity ax times the formal
valence or valences of M" plus y times the formal valence or
valences of M' is equal to z times the formal valence of the
XD.sub.4, X.sub.2D.sub.7 or DXD.sub.4 group.
4. A compound comprising a composition
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X- D.sub.4).sub.z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(DXD.sub.4).sub.z, or
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z, having a
specific surface area of at least 15 m.sup.2/g, wherein A is at
least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" is
any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a.ltoreq.0.1, and x is equal to or
greater than 0, y and z are greater than 0 and have values such
that x, plus y(1-a) times a formal valence or valences of M', plus
ya times a formal valence or valence of M", is equal to z times a
formal valence of the XD.sub.4, X.sub.2D.sub.7, or DXD.sub.4
group.
5. A compound comprising a composition
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X- D.sub.4).sub.z,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, having a
specific surface area of at least 15 m.sup.2/g, wherein A is at
least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any
of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a.ltoreq.0.1, and x, y, and z are
greater than zero and have values such that (1-a).sub.x plus the
quantity ax times the formal valence or valences of M" plus y times
the formal valence or valences of M' is equal to z times the formal
valence of the XD.sub.4, X.sub.2D.sub.7 or DXD.sub.4 group.
6. A compound comprising a composition
(A.sub.b-aM".sub.a).sub.xM'.sub.y(X- D.sub.4).sub.z,
(A.sub.b-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.b-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, having a
specific surface area of at least 15 m.sup.2/g, wherein A is at
least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any
of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a.ltoreq.0.1, a.ltoreq.b.ltoreq.1,
and x, y, and z are greater than zero and have values such that
(b-a).sub.x plus the quantity ax times the formal valence or
valences of M" plus y times the formal valence or valences of M' is
equal to z times the formal valence of the XD.sub.4, X.sub.2D.sub.7
or DXD.sub.4 group.
7. A compound comprising a composition
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X- D.sub.4).sub.z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(DXD.sub.4).sub.z, or
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z, wherein A
is at least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" is
any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a.ltoreq.0.1, and x is equal to or
greater than 0, y and z are greater than 0 and have values such
that x, plus y(1-a) times a formal valence or valences of M', plus
ya times a formal valence or valence of M", is equal to z times a
formal valence of the XD.sub.4, X.sub.2D.sub.7, or DXD.sub.4 group,
crystallizing in an ordered or partially disordered structure of
the olivine (A.sub.xMXO.sub.4), NASICON
(A.sub.x(M',M").sub.2(XO.sub.4).sub.3), VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure-types, and additionally having a molar concentration of
the metals (M'+M") relative to the concentration of the elements X
that exceeds the ideal stoichiometric ratio y/z of the prototype
compounds by at least 0.0001.
8. A compound comprising a composition
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X- D.sub.4).sub.z,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, wherein A
is at least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any
of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a.ltoreq.0.1, and x, y, and z are
greater than zero and have values such that (1-a).sub.x plus the
quantity ax times the formal valence or valences of M" plus y times
the formal valence or valences of M' is equal to z times the formal
valence of the XD.sub.4, X.sub.2D.sub.7 or DXD.sub.4 group,
crystallizing in an ordered or partially disordered structure of
the olivine (A.sub.xMXO.sub.4), NASICON
(A.sub.x(M',M").sub.2(XO.sub.4).sub.3), VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure-types, and additionally having a molar concentration of
the metals (M'+M") relative to the concentration of the elements X
that exceeds the ideal stoichiometric ratio y/z of the prototype
compounds by at least 0.0001.
9. A compound comprising a composition
(A.sub.b-aM".sub.a).sub.xM'.sub.y(X- D.sub.4).sub.z,
(A.sub.b-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.b-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, wherein A
is at least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any
of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a.ltoreq.0.1, a.ltoreq.b.ltoreq.1,
and x, y, and z are greater than zero and have values such that
(b-a).sub.x plus the quantity ax times the formal valence or
valences of M" plus y times the formal valence or valences of M' is
equal to z times the formal valence of the XD.sub.4, X.sub.2D.sub.7
or DXD.sub.4 group, crystallizing in an ordered or partially
disordered structure of the olivine (A.sub.xMXO.sub.4), NASICON
(A.sub.x(M',M").sub.2(XO.sub.4).sub.3), VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure-types, and additionally having a molar concentration of
the metals (M'+M") relative to the concentration of the elements X
that exceeds the ideal stoichiometric ratio y/z of the prototype
compounds by at least 0.0001.
10. The compound of claim 1, wherein the compound can intercalate
at least one of an alkali or hydrogen.
11. The compound of claim 1, wherein M" has a formal valence
greater than 1+ as an ion in the compound.
12. The compound of claim 1, wherein M" is any of aluminum,
titanium, zirconium, niobium, tantalum, tungsten, and
magnesium.
13. The compound of claim 1, wherein A is lithium.
14. The compound of claim 1, wherein X is phosphorus.
15. The compound of claim 1, wherein D is oxygen.
16. The compound of claim 1, wherein M' is any of iron, vanadium,
chromium, manganese, cobalt or nickel.
17. The compound of claim 1, wherein M' is Fe.sup.2+.
18. The compound of claim 1, wherein at least one of M' and M" has
an ionic radius less than the ionic radius of Fe.sup.2+.
19. The compound of claim 1, wherein the compound is substantially
free of silicon.
20. The compound of claim 1, wherein the compound has a crystalline
structure in which at least one of the M' or M" atoms occupy
lattice sites coordinated by anion polyhedra, said polyhedra
forming a continuous network through the structure by sharing at
least one of vertices, corners, edges, or faces.
21. The compound of claim 20, wherein the polyhedra of the
continuous network are filled with transition-metals.
22. The compound of claim 20, wherein the polyhedral units are
octahedra or distorted octahedra.
23. The compound of claim 20, wherein polyhedral units share
corners and edges with other polyhedral units containing M' or
M".
24. The compound of claim 1, wherein the compound is an n-type
conductor.
25. The compound of claim 1, wherein the compound comprises a
mixture of an n-type conductor and a p-type conductor.
26. The compound of claim 1, wherein the compound is a p-type
conductor.
27. The compound of claim 1, wherein A is lithium and during
preparation or use the compound is substantially fully
delithiated.
28. The compound of claim 1, wherein the compound is a p-type
conductor when substantially fully lithiated and an n-type
conductor when substantially fully delithiated.
29. The compound of claim 1, wherein the compound, upon
delithiation, undergoes phase-separation into a substantially
lithiated compound and a substantially delithiated compound, each
of which have an electronic conductivity of at least 10.sup.-6
S/cm.
30. The compound of claim 1, wherein x has a value between zero and
about 1, y is about 1, and z is about 1.
31. The compound of claim 1, wherein x has a value between zero and
about 1, and y is about 1.
32. The compound of claim 1, wherein x has a value between zero and
about 5, y is about 2, and z is about 3.
33. The compound of claim 1, wherein x has a value between zero and
about 2, y is about 1, and z is about 1.
34. The compound of claim 1, wherein x has a value between zero and
about 4, y is about 4, and z is about 3.
35. The compound of claim 1, wherein 0<x/(x+y+z).ltoreq.2/3.
36. The compound of claim 1, wherein the compound has at least one
of an ordered or partially disordered structure of the olivine
(A.sub.xMXO.sub.4), NASICON (A.sub.x(M',M").sub.2(XO.sub.4).sub.3),
VOPO.sub.4, LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure-types.
37. The compound of claim 1, wherein the compound is LiFePO.sub.4
containing additional metals M".
38. The compound of claim 1, wherein the compound has an olivine
structure and contains in crystalline solid solution, amongst the
metals M' and M", simultaneously metal ions of at least one type
that is oxidizable and another that is reducible at 23.degree.
C.
39. The compound of claim 1, wherein the compound has an olivine
structure and contains in crystalline solid solution, amongst the
metals M' and M", simultaneously the metal ions Fe.sup.2+ and
Fe.sup.3+, Mn.sup.2+ and Mn.sup.3+, Co.sup.2+ and Co.sup.3+,
Ni.sup.2+ and Ni.sup.3+, V.sup.2+ and V.sup.3+, or Cr.sup.2+ and
Cr.sup.3+, with the ion of lesser concentration being at least 10
parts per million of the sum of the two ion concentrations.
40. The compound of claim 1, wherein the compound has an olivine
structure, M' includes Fe, and at least one of M' and M" has an
ionic radius less than the ionic radius of Fe.sup.2+.
41. The compound of claim 1, wherein the compound has an olivine
structure, and M" includes at least one metal with ionic radius
less than the average ionic radius of the M' ions.
42. The compound of claim 1, wherein the compound has an olivine
structure with a crystalline solid solution of formula
A.sub.xvac.sub.y(M'.sub.1-aM- ".sub.a)XO.sub.4,
A.sub.x-a-yM".sub.avac.sub.yM'XO.sub.4,
A.sub.x(M'.sub.1-a-yM".sub.avac.sub.y)XO.sub.4 or
A.sub.x-aM".sub.aM'.sub- .1-yvac.sub.yXO.sub.4, wherein vac
represents a vacancy in any of an M1 and M2 site of the primary
crystallites.
43. The compound of claim 1, wherein said compound has the ordered
olivine structure type and A is lithium and is substituted onto a
M2 site of a crystal of the composition at a concentration of at
least about 10.sup.18 per cubic centimeter.
44. The compound of claim 1, wherein said compound has the ordered
olivine structure type and A is lithium and x and a are selected
such that lithium can substitute into an M2 site of a crystal of
the composition as an acceptor defect.
45. The compound of claim 1, wherein the composition is any of
Li.sub.x(M'.sub.1-aM".sub.a)PO.sub.4, Li.sub.xM".sub.aM'PO.sub.4,
Li.sub.x(M'.sub.1-a-yM".sub.aLi.sub.y)PO.sub.4, or
Li.sub.x-aM".sub.aM'.sub.1-yLi.sub.yPO.sub.4.
46. The compound of claim 1, wherein the composition is any of
Li.sub.x(Fe.sub.1-aM".sub.a)PO.sub.4, Li.sub.xM".sub.aFePO.sub.4,
Li.sub.x(Fe.sub.1-a-yM".sub.aLi.sub.y)PO.sub.4, or Li.sub.x-al
M".sub.aFe.sub.1-yLi.sub.yPO.sub.4.
47. The compound of claim 1, wherein the composition is
Li.sub.xvac.sub.1-x(M'.sub.1-aM".sub.a)PO.sub.4,
Li.sub.xM".sub.avac.sub.- 1-a-yM'PO.sub.4,
Li.sub.x(M'.sub.1-a-yM".sub.avac.sub.y)PO.sub.4 or
Li.sub.x-aM".sub.aM".sub.1-yvac.sub.yPO.sub.4, wherein vac
represents a vacancy in a structure of the compound.
48. The compound of claim 1, wherein the composition is
Li.sub.xvac.sub.1-x(Fe.sub.1-aM".sub.a)PO.sub.4,
Li.sub.xM".sub.avac.sub.- 1-a-yFePO.sub.4,
Li.sub.x(Fe.sub.1-a-yM".sub.avac.sub.y)PO.sub.4 or
Li.sub.x-aM".sub.aFe.sub.1-yvac.sub.yPO.sub.4, wherein vac
represents a vacancy in a structure of the compound.
49. The compound of claim 1, wherein the compound has an olivine
structure and at least a portion of A occupies a M1 site.
50. The compound of claim 1, wherein M" is substantially in solid
solution in a crystal structure of the compound.
51. The compound of claim 1, wherein M" is partially in solid
solution in a crystal structure of the compound at a concentration
of at least 0.01 atom % relative to the concentration of M', the
balance appearing as an additional phase.
52. The compound of claim 1, wherein the concentration is at least
0.02 mole %.
53. The compound of claim 1, wherein the concentration is at least
0.05 mole %.
54. The compound of claim 1, wherein the concentration is at least
0.1 mole %.
55. The compound of claim 1, wherein the compound comprises doped
LiFePO.sub.4 in an olivine structure.
56. The compound of claim 1, wherein the compound forms primary
crystallites, at least 50% of which have a smallest dimension less
than 500 nm.
57. The compound of claim 56, wherein the smallest dimension is
less than 200 nm.
58. The compound of claim 56, wherein the smallest dimension is
less than 100 nm.
59. The compound of claim 56, wherein the smallest dimension is
less than 50 nm.
60. The compound of claim 56, wherein the smallest dimension is
less than 20 nm.
61. The compounds of claim 56, wherein the smallest dimension is
less than 10 nm.
62. The compound of claim 56, wherein the primary crystallites form
an interconnected porous network
63. The compound of claim 56, wherein at least about 25% of the
surface area of the primary crystallites is available for contact
with an electrolyte.
64. The compound of claim 56, wherein at least about 50% of the
surface area of the primary crystallites is in contact with an
electrolyte.
65. The compound of claim 1, wherein the compound has a specific
surface area of at least about 10 m.sup.2/g.
66. The compound of claim 1, wherein the specific surface area is
at least about 20 m.sup.2/g.
67. The compound of claim 1, wherein the specific surface area is
at least about 30 m.sup.2/g.
68. The compound of claim 1, wherein the specific surface area is
at least about 40 m.sup.2/g.
69. The compound of claim 1, wherein the specific surface area is
at least about 50 m.sup.2/g.
70. The compound of claim 1, wherein the conductivity is at least
about 10.sup.-7 S/cm.
71. The compound of claim 1, wherein the conductivity is at least
about 10.sup.-6 S/cm.
72. The compound of claim 1, wherein the conductivity is at least
about 10.sup.-5 S/cm.
73. The compound of claim 1, wherein the conductivity is at least
about 10.sup.-4 S/cm.
74. The compound of claim 1, wherein the conductivity is at least
about 10.sup.-3 S/cm.
75. The compound of claim 1, wherein the conductivity is at least
about 10.sup.-2 S/cm.
76. The compound of claim 1, further comprising less than about 15
weight percent of a conductivity-enhancing additive based on the
weight of the composition.
77. The compound of claim 76, wherein the conductivity-enhancing
additive is present in an amount of less than about 10 weight
percent.
78. The compound of claim 76, wherein the conductivity-enhancing
additive is present in an amount of less than about 7 weight
percent.
79. The compound of claim 76, wherein the conductivity-enhancing
additive is present in an amount of less than about 5 weight
percent.
80. The compound of claim 76, wherein the conductivity-enhancing
additive is present in an amount of less than about 3 weight
percent.
81. The compound of claim 76, wherein the conductivity-enhancing
additive is present in an amount of less than about 2 weight
percent.
82. The compound of claim 76, wherein the conductivity-enhancing
additive is present in an amount of less than about 1 weight
percent.
83. The compound of claim 76, wherein the conductivity-enhancing
additive comprises carbon.
84. The compound of claim 1, wherein the compound forms at least
part of an electrode in an electrochemical device.
85. The compound of claim 84, wherein the electrochemical device is
a fuel cell.
86. The compound of claim 1, wherein the compound is a mixed proton
conducting and electronically conducting material.
87. The compound of claim 1, wherein the compound is a gas
separation membrane comprising a mixed proton conducting and
electronically conducting material.
88. The compound of claim 1, wherein the compound is a gas
separation membrane comprising a mixed proton conducting and
electronically conducting material comprising LiFePO.sub.4.
89. The compound of claim 1 formed by mixing an alkali metal or
hydrogen salt, a first-row transition metal compound, a salt of at
least one of phosphorus, sulfur, arsenic, molybdenum and tungsten,
and an ethoxide or methoxide of any of a Group IIA, IIIA, IVA, VA,
VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal; milling
the mixture; and heat treating the mixture at a first temperature
sufficient to form at least one of an olivine, NASICON, VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure.
90. A method of forming a compound, comprising: mixing an alkali
metal or hydrogen salt, a first-row transition metal salt, a salt
of at least one of phosphorus, sulfur, arsenic, silicon, aluminum,
boron, vanadium, molybdenum and tungsten, and a salt of any of a
Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB,
and VIB metal; milling the mixture; and heat treating the mixture
at a temperature between 300-900.degree. C.
91. The method of claim 90, wherein the alkali metal salt is a
metal carbonate.
92. The method of claim 90, wherein the alkali metal salt is
lithium carbonate.
93. The method of claim 90, wherein the alkali metal salt is
LiPO.sub.3.
94. The method of claim 90, wherein the salt of the first-row
transition metal is a metal oxalate.
95. The method of claim 90, wherein the salt of the first-row
transition metal is a metal acetate.
96. The method of claim 90, wherein the salt of the first-row
transition metal is a metal oxide.
97. The method of claim 90, wherein the salt of the first-row
transition metal is iron oxalate.
98. The method of claim 90, wherein the salt of the first-row
transition metal is iron acetate.
99. The method of claim 90, wherein the salt of the first-row
transition metal is iron oxide.
100. The method of claim 90, wherein the salt of at least one of
phosphorus, sulfur, arsenic, silicon, aluminum, boron, vanadium,
molybdenum and tungsten, is ammonium phosphate.
101. The method of claim 90, wherein the salt of at least one of
phosphorus, sulfur, arsenic, silicon, aluminum, boron, vanadium,
molybdenum and tungsten, is LiPO.sub.3.
102. The method of claim 90, wherein the salt of at least one of
phosphorus, sulfur, arsenic, silicon, aluminum, boron, vanadium,
molybdenum and tungsten, is P.sub.2O.sub.5.
103. The method of claim 90, wherein the salt of at least one of
phosphorus, sulfur, arsenic, silicon, aluminum, boron, vanadium,
molybdenum and tungsten, is phosphoric acid.
104. The method of claim 90, wherein the salt of any of a Group
IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and
VIB metal is a metal alkoxide.
105. The method of claim 90, wherein the salt of any of a Group
IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and
VIB metal is a metal oxide.
106. The method of claim 90, wherein the salt of any of a Group
IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and
VIB metal is a metal acetate.
107. The method of claim 90, wherein the salt of any of a Group
IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and
VIB metal is a metal nitrate.
108. The method of claim 90, wherein the salts comprise lithium
carbonate, iron oxalate, ammonium phosphate, and an alkoxide of any
of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal.
109. The method of claim 90, wherein the salts comprise lithium
carbonate, iron oxalate, ammonium phosphate, and an alkoxide of any
of magnesium, aluminum, iron, manganese, titanium, zirconium,
niobium, tantalum, or tungsten.
110. The method of claim 90, wherein the salts comprise lithium
carbonate, iron oxalate, ammonium phosphate, and an oxide of any of
magnesium, aluminum, iron, titanium, zirconium, niobium, tantalum,
or tungsten.
111. The method of claim 90, wherein the salts comprise LiPO.sub.3,
FeO, and an alkoxide of any of a Group IIA, IIIA, IVA, VA, VIA,
VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal.
112. The method of claim 90, wherein-the salts comprise LiPO.sub.3,
FeO, and an oxide of any of a Group IIA, IIIA, IVA, VA, VIA, VIIA,
VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal.
113. The method of claim 90, wherein the salts comprise LiPO.sub.3,
FeO, and an alkoxide of any of magnesium, aluminum, iron,
manganese, titanium, zirconium, niobium, tantalum, or tungsten.
114. The method of claim 90, wherein mixing is performed while the
mixture is under a nonreactive atmosphere.
115. The method of claim 90, wherein heat-treating is performed
while the mixture is under a gaseous atmosphere with an oxygen
partial pressure of less than about 10.sup.-4 atmospheres.
116. The method of claim 90, wherein heat-treating is performed
while the mixture is under a gaseous atmosphere with an oxygen
partial pressure of less than about 10.sup.-5 atmospheres.
117. The method of claim 90, wherein heat-treating is performed
while the mixture is under a gaseous atmosphere with an oxygen
partial pressure of less than about 10.sup.-6 atmospheres.
118. The method of claim 90, wherein heat-treating is performed in
a gaseous atmosphere that is substantially nitrogen gas.
119. The method of claim 90, wherein heat-treating is performed in
a gaseous atmosphere that is substantially argon gas.
120. The method of claim 90, wherein heat-treating is performed in
a gaseous atmosphere that is substantially hydrogen gas.
121. The method of claim 90, wherein heat-treating is performed in
a gaseous atmosphere that is substantially a mixture of nitrogen
and hydrogen gas.
122. The method of claim 90, wherein heat-treating is performed in
a gaseous atmosphere that is substantially a mixture of carbon
monoxide and carbon dioxide gas.
123. The method of claim 90, wherein heat-treating is performed in
a gaseous atmosphere that is substantially nitrogen gas.
124. The method of claim 90, further comprising heat treatment at
two temperatures, the second heat treatment being at a temperature
higher the first temperature.
125. The method of claim 90, further comprising heat treatment at
two temperatures, the first temperature being from 300-400.degree.
C. and the second temperature being from 500-900.degree. C.
126. A method of doping a material to form a lithium or hydrogen
storage compound, comprising: selecting a starting material to be
doped, in conjunction with selection of milling equipment
comprising a dopant for doping the starting material at a
predetermined level of dopant; milling the starting material in the
milling equipment; and recovering from the milling step a material
suitable for forming a lithium or hydrogen storage compound
comprising the starting material doped with the dopant at the
predetermined level.
127. The method of claim 126, wherein the lithium or hydrogen
storage compound is any one of the compounds of claims 1-3.
128. The method of claim 126, wherein the dopant added from the
milling equipment is at least one of zirconium, aluminum, iron,
carbon, or fluorine.
129. The method of claim 126, wherein the dopant comprises at least
zirconium and the milling equipment comprises zirconia milling
media or containers.
130. The method of claim 126, wherein the dopant comprises at least
aluminum and the milling equipment comprises aluminum oxide milling
media or containers.
131. The method of claim 126, wherein the dopant comprises at least
iron and the milling equipment comprises iron or steel milling
media or containers.
132. The method of claim 126, wherein the dopant comprises at least
carbon and the milling equipment comprises polymer milling media or
containers.
133. The method of claim 126, wherein said milling equipment
includes at least one of polypropylene-bearing,
polystyrene-bearing, or polytetrafluoroethylene-bearing milling
media or milling containers.
134. The method of claim 126, wherein the dopant comprises at least
fluorine and the milling equipment comprises fluoropolymer milling
media or containers.
135. An electrode comprising the compound of claim 1 and having a
material energy density that while: charging or discharging at a
rate .gtoreq.30 mA per g of storage compound, is greater than 350
Wh/kg, or charging or discharging at a rate .gtoreq.150 mA per g of
storage compound, is greater than 280 Wh/kg, or charging or
discharging at a rate .gtoreq.300 mA per g of storage compound, is
greater than 270 Wh/kg, or charging or discharging at a rate
.gtoreq.750 mA per g of storage compound, is greater than 250
Wh/kg, or charging or discharging at a rate .gtoreq.1.5 A per g of
storage compound, is greater than 180 Wh/kg, or charging or
discharging at a rate .gtoreq.3 A per g of storage compound, is
greater than 40 Wh/kg, or charging or discharging at a rate
.gtoreq.4.5 A per g of storage compound, is greater than 10
Wh/kg.
136. The electrode composition of claim 135, having a material
energy density that while: charging or discharging at a rate
.gtoreq.30 mA per g of storage compound, is greater than 420 Wh/kg,
or charging or discharging at a rate .gtoreq.150 mA per g of
storage compound, is greater than 400 Wh/kg, or charging or
discharging at a rate .gtoreq.300 mA per g of storage compound, is
greater than 370 Wh/kg, or charging or discharging at a rate
.gtoreq.750 mA per g of storage compound, is greater than 350
Wh/kg, or charging or discharging at a rate .gtoreq.1.5 A per g of
storage compound, is greater than 270 Wh/kg, or charging or
discharging at a rate .gtoreq.3 A per g of storage compound, is
greater than 150 Wh/kg, or charging or discharging at a rate
.gtoreq.4.5 A per g of storage compound, is greater than 80 Wh/kg,
or charging or discharging at a rate .gtoreq.6 A per g of storage
compound, is greater than 35 Wh/kg, or charging or discharging at a
rate .gtoreq.7.5 A per g of storage compound, is greater than 50
Wh/kg, or charging or discharging at a rate .gtoreq.15 A per g of
storage compound, is greater than 10 Wh/kg,
137. The electrode composition of claim 135, having a material
energy density that while: charging or discharging at a rate
.gtoreq.30 mA per g of storage compound, is greater than 475 Wh/kg,
or charging or discharging at a rate .gtoreq.150 mA per g of
storage compound, is greater than 450 Wh/kg, or charging or
discharging at a rate .gtoreq.300 mA per g of storage compound, is
greater than 430 Wh/kg, or charging or discharging at a rate
.gtoreq.750 mA per g of storage compound, is greater than 390
Wh/kg, or charging or discharging at a rate .gtoreq.1.5 A per g of
storage compound, is greater than 350 Wh/kg, or charging or
discharging at a rate .gtoreq.3 A per g of storage compound, is
greater than 300 Wh/kg, or charging or discharging at a rate
.gtoreq.4.5 A per g of storage compound, is greater than 250 Wh/kg,
or charging or discharging at a rate .gtoreq.7.5 A per g of storage
compound, is greater than 150 Wh/kg, or charging or discharging at
a rate .gtoreq.11 A per g of storage compound, is greater than 50
Wh/kg, or charging or discharging at a rate .gtoreq.15 A per g of
storage compound, is greater than 30 Wh/kg.
138. An electrode comprising a lithium storage compound other than
one of ordered or partially ordered rocksalt crystal structure
type, or spinel crystal structure type, or vanadium oxide or
manganese oxide, the electrode having a material energy density
that while: charging or discharging at a rate .gtoreq.800 mA per g
of storage compound, is greater than 250 Wh/kg, or charging or
discharging at a rate .gtoreq.1.5 A per g of storage compound, is
greater than 180 Wh/kg, or charging or discharging at a rate
.gtoreq.3 A per g of storage compound, is greater than 40 Wh/kg, or
charging or discharging at a rate .gtoreq.4.5 A per g of storage
compound, is greater than 10 Wh/kg.
139. The electrode of claim 138, having a material energy density
that while: charging or discharging at a rate .gtoreq.800 mA per g
of storage compound, is greater than 350 Wh/kg, or charging or
discharging at a rate .gtoreq.1.5 A per g of storage compound, is
greater than 270 Wh/kg, or charging or discharging at a rate
.gtoreq.3 A per g of storage compound, is greater than 150 Wh/kg,
or charging or discharging at a rate .gtoreq.4.5 A per g of storage
compound, is greater than 80 Wh/kg, or charging or discharging at a
rate .gtoreq.6 A per g of storage compound, is greater than 35
Wh/kg, or charging or discharging at a rate .gtoreq.7.5 A per g of
storage compound, is greater than 50 Wh/kg, or charging or
discharging at a rate .gtoreq.15 A per g of storage compound, is
greater than 10 Wh/kg,
140. The electrode of claim 138, having a material energy density
that while: charging or discharging at a rate .gtoreq.800 mA per g
of storage compound, is greater than 390 Wh/kg, or charging or
discharging at a rate .gtoreq.1.5 A per g of storage compound, is
greater than 350 Wh/kg, or charging or discharging at a rate
.gtoreq.3 A per g of storage compound, is greater than 300 Wh/kg,
or charging or discharging at a rate .gtoreq.4.5 A per g of storage
compound, is greater than 250 Wh/kg, or charging or discharging at
a rate .gtoreq.7.5 A per g of storage compound, is greater than 150
Wh/kg, or charging or discharging at a rate .gtoreq.11 A per g of
storage compound, is greater than 50 Wh/kg, or charging or
discharging at a rate .gtoreq.15 A per g of storage compound, is
greater than 30 Wh/kg.
141. An electrode comprising the lithium storage compound of claim
1.
142. The electrode of claim 141, wherein the electrode comprises a
sheet or a mesh coated or impregnated with the storage
compound.
143. The electrode of claim 141, wherein the electrode comprises a
metal foil coated one or both sides with the storage compound.
144. The electrode of claim 141, wherein the electrode is a sheet
or mesh of electronically conductive material coated with a loading
of at least 4 mg of said storage compound per square centimeter of
projected area of the sheet or mesh.
145. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with a loading
of at least 8 mg of said storage compound per square centimeter of
projected area of the sheet or mesh.
146. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with a loading
of at least 10 mg of said storage compound per square centimeter of
projected area of the sheet or mesh.
147. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with a loading
of at least 14 mg of said storage compound per square centimeter of
projected area of the sheet or mesh.
148. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with a loading
of at least 20 mg of said storage compound per square centimeter of
projected area of the sheet or mesh.
149. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with said
storage material and has a total thickness of at least 20
micrometers.
150. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with said
storage material and has a total thickness of at least 40
micrometers.
151. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with said
storage material and has a total thickness of at least 60
micrometers.
152. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with said
storage material and has a total thickness of at least 80
micrometers.
153. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with said
storage material and has a total thickness of at least 100
micrometers.
154. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with said
storage material and has a total thickness of at least 150
micrometers.
155. The electrode of claim 141, wherein said electrode is a sheet
or mesh of electronically conductive material coated with said
storage material and has a total thickness of at least 200
micrometers.
156. A storage battery cell comprising: a positive electrode; a
negative electrode; and a separator positioned between the positive
electrode and the negative electrode. wherein at least one of the
positive electrode or negative electrode comprises the compound of
claim 1.
157. The storage battery cell of claim 156 wherein the cell is a
disposable battery cell.
158. The storage battery cell of claim 156 wherein the cell is a
rechargeable battery cell.
159. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 0.25 Wh.
160. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 1 Wh.
161. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 5 Wh.
162. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 10 Wh.
163. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 20 Wh.
164. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 30 Wh.
165. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 40 Wh.
166. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 50 Wh.
167. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge an energy of at least 100 Wh.
168. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric energy density of at least 30
Wh/kg or a volumetric energy density of at least 100 Wh/liter.
169. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric energy density of at least 50
Wh/kg or a volumetric energy density of at least 200 Wh/liter.
170. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric energy density of at least 90
Wh/kg or a volumetric energy density of at least 300 Wh/liter.
171. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric power density of at least 100
W/kg or a volumetric power density of at least 350 W/liter.
172. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric power density of at least 500
W/kg or a volumetric power density of at least 500 W/liter.
173. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric power density of at least
1000 W/kg or a volumetric power density of at least 1000
W/liter.
174. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric power density of at least
2000 W/kg or a volumetric power density of at least 2000
Wh/liter.
175. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric energy density of at least:
30 Wh/kg at a power density of at least 500 W/kg, or 20 Wh/kg at a
power density of at least 1000 W/kg, or 10 Wh/kg at a power density
of at least 1500 W/kg, or 5 Wh/kg at a power density of at least
2000 W/kg, or 2 Wh/kg at a power density of at least 2500 W/kg, or
1 Wh/kg at a power density of at least 3000 W/kg.
176. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric energy density of at least:
50 Wh/kg at a power density of at least 500 W/kg, or 40 Wh/kg at a
power density of at least 1000 W/kg, or 20 Wh/kg at a power density
of at least 2000 W/kg, or 10 Wh/kg at a power density of at least
3000 W/kg, or 4 Wh/kg at a power density of at least 4000 W/kg, or
1 Wh/kg at a power density of at least 5000 W/kg.
177. The storage battery cell of claim 156 wherein the cell
exhibits upon discharge a gravimetric energy density of at least:
80 Wh/kg at a power density of at least 1000 W/kg, or 70 Wh/kg at a
power density of at least 2000 W/kg, or 60 Wh/kg at a power density
of at least 3000 W/kg, or 55 Wh/kg at a power density of at least
4000 W/kg, or 50 Wh/kg at a power density of at least 5000 W/kg, or
30 Wh/kg at a power density of at least 6000 W/kg, or 10 Wh/kg at a
power density of at least 8000 W/kg.
178. The cell of claims 156, wherein the lithium storage compound
is any other than a compound with an ordered or partially
disordered rocksalt or spinel structure type, or vanadium oxide, or
manganese oxide.
Description
RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Application Serial No. 60/343,060,
filed on Dec. 21, 2001, U.S. Provisional Application Serial No.
60/388,721, filed on Jun. 14, 2002, and U.S. Provisional
Application Serial No. 60/412,656, filed on Sep. 20, 2002, the
disclosures of which are herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is directed to transition metal
polyanion oxides that can be used as alkali ion combined materials
and more particularly to lithium-ion intercalating structures that
can be used as electrochemical compounds.
[0004] 2. Description of the Related Art
[0005] The published literature contains many references by those
skilled in the art to the insulating nature of these compounds, and
the limitations on their utility as battery storage materials
thereby created. For example, Gaubicher et al. (J. Gaubicher, T. Le
Mercier, Y. Chabre, J. Angenault, and M. Quarton, "Li/P-VOPO.sub.4:
A New 4 V System for Lithium Batteries," J. Electrochem. Soc.,
146[12] 4375-4379 (1999)) comment with respect to the NASICON
compounds that "unfortunately, the anionic units tend to isolate
the transition elements, which consequently leads to low electronic
conductivity."
[0006] In "Approaching Theoretical Capacity of LiFePO.sub.4 at Room
Temperature at High Rates," H. Huang, S.-C. Yin and L. F. Nazar,
Electrochem. Sol. St. Lett., 4[10] A170-A172 (2001), explain that
"however, owing to their very poor conductivity, initial reports
indicated that Li.sup.+ can only be partially extracted/inserted at
room temperature at modest rates." And, in "Issues and challenges
facing rechargeable lithium batteries," J.-M. Tarascon and M.
Armand, Nature, 414, 359-367 (2001), note that with respect to
these compounds that "one of the main drawbacks with using these
materials is their poor electronic conductivity, and this
limitation had to be overcome through various materials processing
approaches, including the use of carbon coatings, mechanical
grinding or mixing, and low-temperature synthesis routes to obtain
tailored particles."
[0007] Proposed solutions to the poor electronic conductivity have
typically focused entirely on coating with carbon or adding a
significant excess of carbon during synthesis. Coating with carbon
has been described by N. Ravet et al. in "Improved iron-based
cathode materials," Abstr. No. 12, ECS Fall meeting, Hawaii, 1999
and by Morcrette et al. in M. Morcrette, C. Wurm, J. Gaubicher, and
C. Masquelier, "Polyanionic structures as alternative materials for
lithium batteries," Abstr. No. 93, Li Battery Discussion Meeting,
Bordeaux, Archachon, May 27-Jun. 1, 2001. Co-synthesizing with
carbon has been discussed by H. Huang et al. at the Univ. of
Waterloo and by Yamada et al. at the Electrochemical Society Fall
Meeting, San Francisco, Calif., September 2001. However, the
addition of carbon as a conductive additive can lower the
gravimetric and volumetric capacity of the storage material. In
some instances, about 20 wt % carbon is added to the electrode
formulation (approximately 30% by volume). This significant volume
of carbon does not typically store lithium storage at the
potentials at which the polyanion compounds store lithium.
[0008] It is therefore clear and widely acknowledged by those
skilled in the art that poor electronic conductivity is, firstly,
an inherent feature of the lithium-metal-polyanion compounds
discussed herein, and secondly, that this inherent feature limits
the applicability of the materials in lithium storage applications,
including lithium battery electrodes, especially at temperatures
near room temperature. While published literature and patents
describe the addition of various metal additives to such compounds,
they are silent as to whether the critical and enabling property of
improved electronic conductivity can be obtained.
SUMMARY OF THE INVENTION
[0009] The invention provides compounds, methods of forming
compounds, electrodes that comprise compounds and storage battery
cells that include an electrode that comprises a compound.
[0010] In one set of embodiments, a compound is provided. The
compound comprises a composition
A.sub.x(M'.sub.1-aM".sub.a).sub.y(XD4).sub.z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(DXD.sub.4).sub.z, or
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z, wherein A
is at least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" is
any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a .ltoreq.0.1, and x is equal to or
greater than 0, y and z are greater than 0 and have values such
that x, plus y(1-a) times a formal valence or valences of M', plus
ya times a formal valence or valence of M", is equal to z times a
formal valence of the XD.sub.4, X.sub.2D.sub.7, or DXD.sub.4 group.
In some of these embodiments, the compound has a conductivity at
27.degree. C. of at least about 10.sup.-8 S/cm. In some of these
embodiments, the compound has a specific surface area of at least
15 m.sup.2/g. In some of these embodiments, the compound
crystallizes in an ordered or partially disordered structure of the
olivine (A.sub.xMXO.sub.4), NASICON
(A.sub.x(M',M").sub.2(XO.sub.4).sub.3), VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure-types, and has a molar concentration of the metals
(M'+M") relative to the concentration of the elements X that
exceeds the ideal stoichiometric ratio y/z of the prototype
compounds by at least 0.0001.
[0011] In another set of embodiments, a compound is provided. The
compound comprises a composition
(A.sub.1-aM".sub.a).sub.xM'.sub.y(XD.sub.4).sub.z- ,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, wherein A
is at least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any
of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a .ltoreq.0.1, and x, y, and z are
greater than zero and have values such that (1-a)x plus the
quantity ax times the formal valence or valences of M" plus y times
the formal valence or valences of M' is equal to z tines the formal
valence of the XD.sub.4, X.sub.2D.sub.7 or DXD.sub.4 group. In some
of these embodiments, the compound has a conductivity at 27.degree.
C. of at least about 10.sup.-8 S/cm. In some of these embodiments,
the compound has a specific surface area of at least 15 m.sup.2/g.
In some of these embodiments, the compound crystallizes in an
ordered or partially disordered structure of the olivine
(A.sub.xMXO.sub.4), NASICON
(A.sub.x,(M',M").sub.2(XO.sub.4).sub.3), VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure-types, and has a molar concentration of the metals
(M'+M") relative to the concentration of the elements X that
exceeds the ideal stoichiometric ratio y/z of the prototype
compounds by at least 0.0001.
[0012] In another embodiment, a compound is provided. The compound
comprises a composition
(A.sub.b-aM".sub.a).sub.xM'.sub.y(XD.sub.4).sub.z- ,
(A.sub.b-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.b-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z, wherein A
is at least one of an alkali metal or hydrogen, M' is a first-row
transition metal, X is at least one of phosphorus, sulfur, arsenic,
boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any
of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen,
carbon, or a halogen, 0.0001<a.ltoreq.0.1, a.ltoreq.b.ltoreq.1,
and x, y, and z are greater than zero and have values such that
(b-a).sub.x plus the quantity ax times the formal valence or
valences of M" plus y times the formal valence or valences of M' is
equal to z times the formal valence of the XD.sub.4, X.sub.2D.sub.7
or DXD.sub.4 group. In some of these embodiments, the compound has
a conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm.
In some of these embodiments, the compound has a specific surface
area of at least 15 m.sup.2/g. In some of these embodiments, the
compound crystallizes in an ordered or partially disordered
structure of the olivine (A.sub.xMXO.sub.4), NASICON
(A.sub.x(M',M").sub.2(XO.sub.4).sub.3), VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3
structure-types, and has a molar concentration of the metals
(M'+M") relative to the concentration of the elements X that
exceeds the ideal stoichiometric ratio y/z of the prototype
compounds by at least 0.0001.
[0013] In another set of embodiments, methods of forming a compound
are provided. The methods include mixing an alkali metal or
hydrogen salt, a first-row transition metal salt, a salt of at
least one of phosphorus, sulfur, arsenic, silicon, aluminum, boron,
vanadium, molybdenum and tungsten, and a salt of any of a Group
IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and
VIB metal; milling the mixture; and heat treating the mixture at a
temperature between 300-900.degree. C.
[0014] In another set of embodiments, methods of doping a material
to form a lithium or hydrogen storage compound are provided. The
methods include selecting a starting material to be doped, in
conjunction with selection of milling equipment comprising a dopant
for doping the starting material at a predetermined level of
dopant. The methods further include milling the starting material
in the milling equipment; and recovering from the milling step a
material suitable for forming a lithium or hydrogen storage
compound comprising the starting material doped with the dopant at
the predetermined level.
[0015] In another set of embodiments, an electrode comprising a
lithium storage compound is provided. The electrode can comprise
any of the compounds described above and has a material energy
density (i.e., voltage vs. Li.times.charge capacity) that while:
charging or discharging at a rate .gtoreq.30 mA per g of storage
compound, is greater than 350 Wh/kg; or, charging or discharging at
a rate .gtoreq.150 mA per g of storage compound, is greater than
280 Wh/kg; or, charging or discharging at a rate .gtoreq.300 mA per
g of storage compound, is greater than 270 Wh/kg; or, charging or
discharging at a rate .gtoreq.750 mA per g of storage compound, is
greater than 250 Wh/kg; or, charging or discharging at a rate
.gtoreq.1.5 A per g of storage compound, is greater than 180 Wh/kg;
or, charging or discharging at a rate .gtoreq.3 A per g of storage
compound, is greater than 40 Wh/kg; or, charging or discharging at
a rate .gtoreq.4.5 A per g of storage compound, is greater than 10
Wh/kg.
[0016] In another set of embodiments, an electrode comprising a
lithium storage compound is provided. The lithium storage compound
is a compound other than one of ordered or partially ordered
rocksalt crystal structure type, or spinel crystal structure type,
or vanadium oxide or manganese oxide. The compound has a material
energy density (i.e., voltage vs. Li.times.charge capacity) that
while: charging or discharging at a rate .gtoreq.800 mA per g of
storage compound, is greater than 250 Wh/kg; or, charging or
discharging at a rate .gtoreq.1.5 A per g of storage compound, is
greater than 180 Wh/kg; or, charging or discharging at a rate
.gtoreq.3 A per g of storage compound, is greater than 40 Wh/kg;
or, charging or discharging at a rate .gtoreq.4.5 A per g of
storage compound, is greater than 10 Wh/kg.
[0017] In another set of embodiments, an electrode is provided. The
electrodes includes a current collector comprising any of the
compounds described above.
[0018] In another set of embodiments, a storage battery cell is
provided. The storage battery comprises a positive electrode, a
negative electrode and a separator positioned between the positive
electrode and the negative electrode. At least one of the positive
electrode or negative electrode comprises any of the compounds
described above.
[0019] Other embodiments and novel features of the invention should
become apparent from the following detailed description when
considered in conjunction with the accompanying drawings. In cases
of conflict between an incorporated reference and the present
specification, the present specification shall control.
BRIEF DESCRIPTION OF DRAWINGS
[0020] Preferred, non-limiting embodiments of the present invention
will be described by way of example with reference to the
accompanying drawings, in which:
[0021] FIG. 1 is a copy of an TEM image of a compound with 0.1% Ti
doping, prepared according to the method substantially described in
Example 1 and heat treated at 600.degree. C. in argon for
twenty-four hours, showing that the primary crystallite size is
about 100-200 nm and that the primary crystallites are aggregated
into larger particles; and showing that there is no surface coating
or other continuous phase which could provide improved electronic
conductivity; thus, the improved electronic conductivity is likely
due to an improvement in the compound itself;
[0022] FIG. 2 are copies of scanning transmission electron
microscope images and energy-dispersive x-ray composition maps of a
1% Ti-doped sample prepared according to the method substantially
described in Example 1 and heat treated at 600.degree. C. in
nitrogen for twenty-four hours or 800.degree. C. in argon for
sixteen hours. In the sample heat treated at 600.degree. C., there
is detectable Ti in solid solution in the compound as well as an
excess of Ti appearing as an additional phase whereas the sample
heat treated at 800.degree. C. shows no Ti detectable in the phase
itself, thus showing that the solid solubility of Ti under these
conditions is likely less than about 0.1%;
[0023] FIG. 3 are copies of scanning transmission electron
microscope images and energy-dispersive x-ray composition maps of
an 0.2% Nb-doped sample prepared according to the method
substantially described in Example 1 and heat treated at
600.degree. C. for twenty-four hours, 700.degree. C. for twenty
hours, and 800.degree. C. for fifteen hours, all in argon, showing
that in the sample heat treated at 600.degree. C., substantial
amounts of Nb can be detected within the LiFePO.sub.4 grains and a
Nb-rich additional phase is substantially absent; in the samples
heat treated at 700.degree. C. and 800.degree. C., substantially
less Nb is detectable in the grains and Nb-rich additional phase
has appeared, and thus showing that the solubility of Nb is at
least about 0.2% when the material is prepared according to Example
1 and heat treated at 600.degree. C., whereas heat treating at a
temperature of 700.degree. C., or greater, causes exsolution of
Nb;
[0024] FIG. 4 is a graph showing x-ray diffraction patterns of
materials prepared according to Example 1, undoped samples and
samples containing 1% Ti, 1% Zr, 2% Ti, and 2% Zr, heat treated at
600.degree. C. in nitrogen for twenty-four hours, showing that
additional phases can be detectable in all of the doped samples and
thus that, the solubility limit of the dopants is less than 1%
under these preparation conditions; the composition heat treated in
argon and nitrogen being substantially similar to that shown in
FIG. 15; thus showing that multiple non-oxidizing gas atmospheres
can be used to prepare the electronically conductive materials of
the invention;
[0025] FIG. 5 is a copy of TEM images of a powder of nominal
composition LiFe.sub.0.99Zr.sub.0.01PO.sub.4 and prepared according
to the Example 1, showing crystalline particles in which lattice
fringes are visible and which do not possess a distinguishable
surface phase of another material such as carbon;
[0026] FIGS. 6A and 6B show X-ray diffraction patterns of various
powders showing the effect of cation stoichiometry on dopant
solid-solubility. FIG. 35A shows powders containing 1 atom % dopant
in the stoichiometry Li.sub.1-xM.sub.xFePO.sub.4 are single-phase
by XRD and TEM/STEM analysis. FIG. 35B shows powders containing 1
atom % dopant in the stoichiometry LiFe.sub.1-xM.sub.xPO.sub.4 show
Li.sub.3PO.sub.4 precipitation by XRD, and secondary phases
enriched in the dopant by TEM/STEM (not shown);
[0027] FIGS. 7A-7D show elemental maps obtained by STEM of a powder
of composition Li.sub.0.99Nb.sub.0.01FePO.sub.4 (fired 600.degree.
C., 20 h, in argon) which illustrate the uniform dopant solid
solution observed in compositions of stoichiometry
Li.sub.1-xM.sub.xFePO.sub.4;
[0028] FIGS. 8 and 9 are graphs showing the conductivity of doped
and undoped samples as a function of temperature;
[0029] FIG. 10 shows backscattered electron images of the polished
cross-section of two Nb-doped and one undoped pellet sintered to
high density;
[0030] FIG. 11 is the configuration of a four-point microcontact
measurement performed to determine the electronic conductivity of
samples;
[0031] FIG. 12 is the electrical conductivity measured at several
locations within each of the three samples of FIG. 10;
[0032] FIG. 13 shows bright-field TEM images of powders of 1% Nb
and 1% Zr doping level and prepared according to the invention;
[0033] FIG. 14 shows a TEM image of a conductive 1% Nb doped
composition fired at 600C, showing a particle of incompletely
reacted precursor and crystallized olivine phase, and
energy-dispersive X-ray spectra taken with a focused electron probe
at the locations indicated, showing that carbon is enriched within
the particle of unreacted precursor and not detected within several
locations of the olivine phase;
[0034] FIGS. 15 and 16 show high resolution TEM images of a
conductive 1% Nb doped composition fired at 600C, in which lattice
fringes are visible in crystallites of olivine phase, and showing
the absence of a significant surface coating of another
material;
[0035] FIG. 17A shows a first electrochemical cycle for an
electrode prepared using a Nb-doped composition, and tested against
a lithium metal negative electrode in a laboratory cell using a
nonaqueous liquid electrolyte. FIG. 17B shows capacity vs. cycle
number for this electrode at a 1C rate (150 mA/g). FIG. 17C shows
the coulombic efficiency vs. cycle number at 1C rate (150
mA/g);
[0036] FIGS. 18A and 18B show electrochemical test data for
electronically conductive olivine of composition
Li.sub.0.99Zr.sub.0.01FePO.sub.4 S in a conventional lithium
battery electrode design (78 wt % cathode-active material, 10 wt %
Super PTM carbon, 12 wt % PVdF binder; 2.5 mg/cm.sup.2 loading)
with a lithium metal negative electrode and nonaqueous liquid
electrolyte. FIG. 18A shows results of cycle testing which
indicates high and stable reversible capacity for more than 150
cycles at a variety of current rates. Significant capacity with
high coulombic efficiency (>99.5%) is retained at rates as high
as 3225 mA/g (21.5C). FIG. 18B shows charge-discharge curves
indicating little polarization even at the highest current rates,
attributed to the high electronic conductivity and high specific
surface area of the olivine powder;
[0037] FIG. 19 shows discharge curves for continuous cycling
between 2-4.2V for an electrode made using
Li.sub.0.99Zr.sub.0.01FePO.sub.4 powder and tested to discharge
rates of 66.2C (9.93 A/g) at a temperature of 42.degree. C. in a
conventional cell design using a lithium metal negative electrode
and nonaqueous liquid electrolyte;
[0038] FIG. 20 shows discharge curves for constant-current
constant-voltage cycling between 2-3.8V for an electrode made using
Li.sub.0.99Zr.sub.0.01FePO.sub.4 powder and tested to discharge
rates of 200C (30 A/g) at a temperature of 22.degree. C. in a
conventional cell design using a lithium metal negative electrode
and nonaqueous liquid electrolyte;
[0039] FIG. 21 shows discharge capacity vs. discharge rate curves
for several electrodes formulated using
Li.sub.0.99Zr.sub.0.01FePO.sub.4 powder heat treated at 600.degree.
C. or 700.degree. C., and tested to high discharge rates greater
than 60C (9 A/g) at 22-23.degree. C. in a conventional cell design
using a lithium metal negative electrode and nonaqueous liquid
electrolyte;
[0040] FIG. 22 shows discharge capacity vs. discharge rate curves
for two electrodes formulated using undoped LiFePO.sub.4 powder
heat treated at 700.degree. C., and tested at 23.degree. C. in a
conventional cell design using a lithium metal negative electrode
and nonaqueous liquid electrolyte;
[0041] FIG. 23 shows discharge capacity vs. discharge rate curves
for several LiFePO4 electrodes described in published literature,
compared to an electrode of the invention containing
Li.sub.0.99Zr.sub.0.01FePO.sub.4 powder, showing the markedly
higher discharge capacity available at high discharge rates of the
electrodes of the invention;
[0042] FIG. 24 shows the discharge energy density in mAh/g vs. the
current density in mA/g for an electrode formulated using
Li.sub.0.99Zr.sub.0.01F- ePO.sub.4 powder and measured at a
temperature of 22.degree. C.;
[0043] FIG. 25 shows the discharge energy density in mAh/g vs. the
current density in mA/g for an electrode formulated using
Li.sub.0.99Zr.sub.0.01F- ePO.sub.4 powder and measured at
temperatures of 23, 31, and 42.degree. C.;
[0044] FIG. 26 shows the discharge energy density in mAh/g vs. the
current density in mA/g for an electrode formulated using
Li(Fe.sub.0.98Ti.sub.0.- 02)PO.sub.4 powder and measured at
23.degree. C.;
[0045] FIG. 27 shows the discharge energy density in mAh/g vs. the
current density in mA/g for an electrode formulated using undoped
LiFePO4 and measured at temperatures of 23, 31, and 42.degree.
C.
[0046] FIG. 28 shows a Ragone plot of log power density vs. log
energy density for storage battery cells based on the lithium
storage materials and electrodes of the invention, compared with
other storage battery technology, showing the improved power
density that is available while still having high energy
density.
[0047] FIG. 29 shows a schematic storage battery cell according to
one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0048] LiFePO.sub.4 and Li(Mn,Fe)PO.sub.4 are ordered olivine
structure compounds also known as the mineral triphylite. They
belong to the general group known as polyanion compounds with
tetrahedral "anion" structural units (XO.sub.4).sup.n-, along with
oxygen octahedra occupied by a transition metal M, and can include
compounds of Li.sub.xMXO.sub.4 (olivine),
Li.sub.xM.sub.2(XO.sub.4).sub.3 (NASICON), VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3 structure,
and structures related to these by having additional metal ions
occupying interstitial sites, symmetry-changing displacements, or
minor changes in the connectivity of polyhedra. Here, X is
comprised of a metal that can occupy tetrahedral sites within the
polyanion groups and has a significant covalent bonding character.
X can be P, S, As, Mo, W, Al, Si, or B. According to the present
invention, these compounds can be used as lithium storage electrode
materials because of their high lithium-insertion potential
(relative to lithium metal), high theoretical capacity, low cost,
ease of synthesis, and stability when used with common organic
electrolyte systems. Despite these characteristics, it has been
widely recognized that one of the limitations of this series of
compounds is their low electronic conductivity, which greatly
limits the practicality of these materials in battery systems.
Related compounds such as (Mg,Fe)SiO.sub.4 are also electronic
insulators at an near room temperature, and only have appreciable
electronic conductivity at greatly elevated temperatures.
[0049] It is therefore a surprising and unexpected discovery that
certain compositions of LiFePO.sub.4, prepared from starting
materials of lithium salts, iron compounds, and phosphorous salts,
including but not limited to, lithium carbonate, ammonium
phosphate, and iron oxalate, and to which a low additional
concentration of a metal supervalent to Li, such as, but not
limited to, Mg, Al, Ti, Fe, Mn, Zr, Nb, Ta, and W, such as in the
form of a metal oxide or metal alkoxide, have been added, and which
is heat treated (HT) at a certain temperature range and atmosphere,
exhibit increased electronic conductivity at and near room
temperature to render the compounds useful as lithium storage
materials.
[0050] As used herein, the electrical conductivity of materials
will be given in units of S/cm, electrical resistivity in units of
ohm-cm (.OMEGA.-cm), resistance in ohms (.OMEGA.), charge and
discharge capacity in units of ampere hours per kilogram of the
storage material (Ah/kg) or milliampere hour per gram of storage
material (mAh/g), charge and discharge rate in units of both
milliamperes per gram of the storage compound (mA/g), and C rate.
When given in units of C rate, the C rate is defined as the inverse
of the time, in hours, necessary to utilize the full capacity of
the battery measured at a slow rate. A rate of 1C refers to a time
of one hour; a rate of 2C refers to a time of half an hour, a rate
of C/2 refers to a time of two hours, and so forth. Typically, the
C rate is computed from the rate, in mA/g, relative to the capacity
of the compound or battery measured at a lower rate of C/5 or less.
For example, in some examples herein the nominal capacity of a
doped LiFePO.sub.4 compound at low rate is about 150 mAh/g, and
therefore a rate of 1C corresponds to a current rate of 150 mA/g, a
rate of C/5 corresponds to 30 mA/g, a rate of 5C corresponds to 750
mA/g, and so forth.
[0051] In one aspect, the present invention is directed to
increasing the electronic conductivity of transition metal
polyanion compounds so that they can be used as alkali ion storage
materials, for example, rechargeable lithium ion batteries. The
compounds of the invention have electronic conductivities near room
temperature, for example at a temperature of 22.degree.
C.-27.degree. C., of at least about 10.sup.-8 S/cm. However, in
some cases, the conductivity is at least about at least about
10.sup.-7 S/cm, in other cases, at least about 10.sup.-6 S/cm, in
yet other cases, at least about 10.sup.-5 S/cm, in still other
cases, at least about 10.sup.-4 S/cm, in preferred cases, at least
about 10.sup.-3 S/cm, and in more preferred cases, at least about
10.sup.-2S/cm. Where elements and groups in the Periodic Table are
referred to, the Periodic Table catalog number S-18806, published
by the Sargent-Welch company in 1994, is used as a reference.
[0052] In one aspect, the present invention is directed to
increasing the electronic conductivity of transition metal
polyanion compounds so that they can be used as alkali ion storage
materials, for example, rechargeable lithium ion batteries, without
adding excessive amounts of an additional conductive compound such
as carbon. Accordingly, the present invention can include
conductivity-enhancing additives, such as but not limited to
conductive carbon black, at, for example, less than about 15 weight
percent, or in some cases, less than about 10 weight percent, in
other cases, less than about 7 weight percent, in other cases, less
than 3 weight percent, in other cases, less than 1 weight percent
and, in some cases, no conductivity-enhancing additive.
[0053] In another aspect, the present invention is directed to
decreasing the particle or crystallite size, or increasing the
specific surface area (typically given in square meters per gram of
the material, M.sup.2/g, and measured by such methods as the
Brunauer-Emmett-Teller (BET) gas adsorption method) of transition
metal polyanion compounds in order to provide improved
electrochemical energy storage, including improved charge storage
capacity, improved energy density and power density when used in an
electrochemical cell, and improved cycle life when the
electrochemical cell is reversibly charged and discharged.
Compositions are provided for compounds of high specific surface
area, including those that are substantially fully crystallized, or
those that have substantial electronic conductivity. The materials
of the invention have specific surface areas of at least 15
m.sup.2/g. However, in other cases they have specific surface areas
of at least 20 m.sup.2/g, in other cases at least 30 m.sup.2/g, and
in other cases at least 40 m.sup.2/g.
[0054] In another aspect, the present invention provides methods
for preparing the transition metal polyanion compounds of the
invention, including compounds with substantial electronic
conductivity and/or high specific surface area and small particle
or crystallite size.
[0055] In another aspect, the invention comprises storage
electrodes, including those using the transition metal polyanion
compounds of the invention. Such storage electrodes have useful
properties for electrochemical energy storage including having high
storage energy density, high power density, and long cycle life
when used reversibly in an electrochemical device. Formulations of
and methods for preparing said electrodes are provided.
[0056] In another aspect, the invention comprises storage battery
cells, including those using the transition metal polyanion
compounds of the invention. Such cells have useful energy storage
characteristics including high energy density and high power
density, and long cycle life.
[0057] Electronic Conductivity
[0058] In one embodiment, the present invention provides an
electrochemical device comprising an electrode comprising a
compound with a formula Li.sub.xFe.sub.1-aM".sub.aPO.sub.4, and a
conductivity at 27.degree. C., of at least about 10.sup.-8 S/cm.
However, in some cases, the conductivity is at least about at least
about 10.sup.-7 S/cm, in other cases, at least about 10.sup.-6
S/cm, in yet other cases, at least about 10.sup.-5 S/cm, in still
other cases, at least about 10.sup.-4 S/cm, in preferred cases, at
least about 10.sup.-3 S/cm, and in more preferred cases, at least
about 10.sup.2S/cm.
[0059] In another embodiment, the present invention provides an
electrochemical device comprising an electrode comprising a
compound with a formula Li.sub.xFe.sub.1-aM".sub.aPO.sub.4, the
compound having a gravimetric capacity of at least about 80 mAh/g
while the device is charging/discharging at greater than about C
rate. However, in some embodiments, the capacity is at least about
100 mAh/g, or in other embodiments, at least about 120 mAh/g, in
preferred embodiments, at least about 150 mAh/g, and in still other
embodiments, at least about 160 mAh/g. The present invention can,
in some embodiments, also provide a capacity up to the theoretical
gravimetric capacity of the compound.
[0060] In another embodiment, the present invention provides an
electrochemical device comprising an electrode comprising a
compound with a formula Li.sub.x-aM".sub.aFePO.sub.4.
[0061] In another embodiment, the present invention provides an
electrochemical device comprising an electrode comprising a
compound with a formula Li.sub.x-aM".sub.aFePO.sub.4, and a
conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm.
However, in some cases, the conductivity is at least about at least
about 10.sup.-7 S/cm, in other cases, at least about 10.sup.-6
S/cm, in yet other cases, at least about 10.sup.-5 S/cm, in still
other cases, at least about 10.sup.-4 S/cm, and in preferred cases,
at least about 10.sup.-3 S/cm, and in more preferred cases, at
least about 10.sup.-2 S/cm.
[0062] In another embodiment, the present invention provides an
electrochemical device comprising an electrode comprising a
compound with a formula Li.sub.x-aM".sub.aFePO.sub.4, the compound
having a gravimetric capacity of at least about 80 mAh/g while the
device is charging/discharging at greater than about C rate.
However, in some embodiments, the capacity is at least about 100
mAh/g, or in other embodiments, at least about 120 mAh/g, in
preferred embodiments, at least about 150 mAh/g and in still other
preferred embodiments, at least about 170 mAh/g. The present
invention can, in some embodiments, also provide a capacity up to
the theoretical gravimetric capacity of the compound.
[0063] According to one embodiment, a composition comprising a
compound with a formula
A.sub.x(M'.sub.1-aM".sub.a).sub.y(XD.sub.4).sub.z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(DXD.sub.4).sub.z, or
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z, has a
conductivity at about 27.degree. C. of at least about 10.sup.-8
S/cm, wherein A is at least one of an alkali metal and hydrogen, M'
is a first-row transition metal, X is at least one of phosphorus,
sulfur, arsenic, molybdenum and tungsten, M" is any of a Group IIA,
IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB
metal, D is at least one of oxygen, nitrogen, carbon, or a halogen,
0.0001<a.ltoreq.0.1, and x, y, and z have values such that x
plus the quantity y(1-a) times a formal valence or valences of M',
plus the quantity ya times a formal valence or valence of M", is
equal to z times a formal valence of the XD.sub.4, X.sub.2D.sub.7,
or DXD.sub.4 group. x, y, and z are typically greater than 0. The
conductivity of the compound can be at least about 10.sup.-5 S/cm,
at least about 10.sup.-4 S/cm, and, in some cases, at least about
10.sup.-2 S/cm. In some embodiments, A is lithium and x/(x+y+z) can
range from about zero to about one third, or about zero to about
two thirds. In one embodiment, X is phosphorus, while in other
embodiments, M' is iron. M" can be any of aluminum, titanium,
zirconium, niobium, tantalum, tungsten, or magnesium. M" can be
substantially in solid solution in the crystal structure of the
compound. Typically, the compound has at least one of an olivine,
NASICON, VOPO.sub.4, LiFe(P.sub.2O.sub.7) or
Fe.sub.4(P.sub.2O.sub.7).sub.3 structure, or mixtures thereof.
[0064] In some embodiments, the compound is LiFePO.sub.4.
[0065] In some embodiments, M" is at least partially in solid
solution in the crystal structure of the compound at a
concentration of at least 0.01 mole % relative to the concentration
of M', the balance appearing as an additional phase, at least 0.02
mole % relative to the concentration of M', the balance appearing
as an additional phase, and in yet other embodiments, at least 0.05
mole % relative to the concentration of M', the balance appearing
as an additional phase and, in still other embodiments, at a
concentration of at least 0.1 mole % relative to the concentration
of M', the balance appearing as an additional phase.
[0066] In some embodiments, the compound can be formed as particles
or crystallites wherein at least 50% of which have a smallest
dimension that is less than about 500 nm. However, in some cases,
the smallest dimension is less than 200 nm, in yet other cases, the
smallest dimension is less than 100 nm, in still other cases, the
smallest dimension is less than 50 nm, in still other cases, the
smallest dimension is less than 20 nm, and in still other cases,
the smallest dimension is less than 10 nm. In some embodiments, the
compound forms an interconnected porous network comprising
crystallites with a specific surface area of at least about 10
m.sup.2/g. However, in some cases, the specific surface area is at
least about 20 m.sup.2/g, in other cases, the specific surface area
is at least about 30 m.sup.2/g, in other cases, the specific
surface area is at least about 40 m.sup.2/g, in other cases, the
specific surface area is at least about 50 m.sup.2/g. Smallest
dimension, in this context, means a cross-section. In some cases,
the present invention provides a compound with a formula
(A.sub.1-aM".sub.a).sub.xM'.sub.y(XD.sub.4).sub.z,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7), that has a
conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm,
wherein A is at least one of an alkali metal and hydrogen, M' is a
first-row transition metal, X is at least one of phosphorus,
sulfur, arsenic, molybdenum, and tungsten, M" any of a Group IIA,
IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB
metal, D is at least one of oxygen, nitrogen, carbon, or a halogen,
0.0002<a>0.1, and x, y, and z have values such that
(1-a).sub.x plus the quantity ax times the formal valence or
valences of M" plus y times the formal valence or valences of M' is
equal to z times the formal valence of the XD.sub.4, X.sub.2D.sub.7
or DXD.sub.4 group. x, y, and z are typically greater than zero.
The conductivity of the compound can be at least about 10.sup.-5
S/cm, at least about 10.sup.-4 S/cm, and, in some cases, at least
about 10.sup.-2 S/cm. In some embodiments, A is lithium and
x/(x+y+z) can range from about zero to about one third. In one
embodiment, X is phosphorus, while in other embodiments, M' is
iron. M" can be any of aluminum, titanium, zirconium, niobium,
tantalum, tungsten, or magnesium. M" can be substantially in solid
solution in the crystal structure of the compound. Typically, the
compound has at least one of an olivine, NASICON, VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3 structure,
or mixtures thereof. In some embodiments, the compound is
LiFePO.sub.4. In some embodiments, M" is at least partially in
solid solution in the crystal structure of the compound at a
concentration of at least 0.01 mole % relative to the concentration
of M', the balance appearing as an additional phase, at least 0.02
mole % relative to the concentration of M', the balance appearing
as an additional phase, and in yet other embodiments, at least 0.05
mole % relative to the concentration of M', the balance appearing
as an additional phase and, in still other embodiments, at a
concentration of at least 0.1 mole % relative to the concentration
of M', the balance appearing as an additional phase.
[0067] In some embodiments, the electronically conductive lithium
transition metal phosphate olivine compound has a suitable
electronic conductivity greater than about 10.sup.-8 S/cm. The
electronically conductive lithium transition metal phosphate
compound can be a composition Li.sub.x(M.sub.1-aM".sub.a)PO.sub.4
or Li.sub.x-aM".sub.aM'PO.sub.4, and can crystallize in the
ordered-olivine or triphylite structure, or a structure related to
the ordered olivine or triphylite structure with small
displacements of atoms without substantial changes in the
coordination number of anions around cations, or cations around
anions. In such compounds Li.sup.+ substantially occupies the
octahedral site typically designated as M1, and a substantially
divalent cation M' substantially occupies the
octahedrally-coordinated site typically designated as M2, as
described in the olivine structure given in "Crystal Chemistry of
Silicate Minerals of Geophysical Interest," by J. J. Papike and M.
Cameron, Reviews of Geophysics and Space Physics, Vol. 14, No. 1,
pages 37-80, 1976. In some embodiments, the exchange of Li and the
metal M' between their respective sites in a perfectly ordered
olivine structure is allowed so that M' may occupy either site. M'
is typically one or more of the first-row transition metals, V, Cr,
Mn, Fe, Co, or Ni. M" is typically a metal with formal valence
greater than I+as an ion in the crystal structure.
[0068] In some embodiments, M', M", x, and a are selected such that
the compound is a crystalline compound that has in solid solution
charge compensating vacancy defects to preserve overall charge
neutrality in the compound. In the compositions of type
Li.sub.x(M.sub.1-aM".sub.a)PO.sub.4 or
Li.sub.x-aM".sub.aM'PO.sub.4, this condition can be achieved when a
times the formal valence of M" plus (1-a) times the formal valence
of M' plus x is greater than 3+, necessitating an additional cation
deficiency to maintain charge neutrality, such that the crystal
composition is Li.sub.x(M'.sub.1-a-yM".sub.avac.sub.y)PO.sub.4 or
Li.sub.x-aM".sub.aM'.sub.yvac.sub.yPO.sub.4, where vac is a
vacancy. In the language of defect chemistry, the dopant can be
supervalent and can be added under conditions of temperature and
oxygen activity that promote ionic compensation of the donor,
resulting in nonstoichiometry. The vacancies can occupy either M1
or M2 sites. When x<1, the compound also has additional cation
vacancies on the M1 site in a crystalline solid solution, said
vacancies being compensated by increasing the oxidation state of M"
or M'. In order to increase the electronic conductivity usefully, a
suitable concentration of said cation vacancies should be greater
than or equal to 10.sup.18 per cubic centimeter.
[0069] In some cases, the compound has an olivine structure and
contains in crystalline solid solution, amongst the metals M' and
M", simultaneously the metal ions Fe.sup.2+ and Fe.sup.3+,
Mn.sup.2+ and Mn.sup.3+, Co.sup.2+ and Co.sup.3+, Ni.sup.2+ and
Ni.sup.3+, V.sup.2+ and V.sup.3+, or Cr.sup.2+ and Cr.sup.3+, with
the ion of lesser concentration being at least 10 parts per million
of the sum of the two ion concentrations.
[0070] In some embodiments, the compound has an ordered olivine
structure and A, M', M", x, and a are selected such that there can
be Li substituted onto M2 sites as an acceptor defect. In the
compositions of type Li.sub.x(M'.sub.1-aM".sub.a)PO.sub.4 or
Li.sub.x-aM".sub.aM'PO.sub.4- , typical corresponding crystal
compositions are Li.sub.x(M'.sub.1-a-yM".s- ub.aLi.sub.y)PO.sub.4
or Li.sub.x-aM".sub.aM'.sub.1-yLi.sub.yPO.sub.4. In this instance,
the subvalent Li substituted onto M2 sites for M' or M" can act as
an acceptor defect. In order to increase the electronic
conductivity usefully, a suitable concentration of said Li on M2
sites should be greater than or equal to 10.sup.18 per cubic
centimeter.
[0071] In some embodiments, the present invention provides a p-type
semiconducting composition, Li.sub.x(M'.sub.1-aM".sub.a)PO.sub.4,
Li.sub.xM".sub.aM'PO.sub.4,
Li.sub.x(M'.sub.1-a-yM".sub.avac.sub.y)PO.sub- .4,
Li.sub.x-aM".sub.aM'.sub.1-yvac.sub.yPO.sub.4,
Li.sub.x(M'.sub.1-a-yM"- .sub.aLi.sub.y)PO.sub.4 or
Li.sub.x-aM".sub.aM'.sub.1-yLi.sub.yPO.sub.4. M" is a group IIA,
IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB
element of the Periodic Table (catalog number S-18806, published by
the Sargent-Welch company in 1994.) Magnesium is an example of a
dopant from Group IIA, Y is an example of a dopant from Group IIIA,
Ti and Zr are examples of dopants from Group IVA, Nb and Ta are
examples of dopants from Group VA, W is an example of a dopant from
Group VIA, Fe is an example of a metal from Group VIIIA, and Al is
an example of a dopant from Group IIIB.
[0072] x can have a value between zero and 1.1 in the initially
prepared material, and during its use as an lithium ion storage
compound, x can vary between about zero and about 1.1. a can have a
value between about 0.0001 and 0.1. In some embodiments, out of the
total amount a of M", at least 0.0001 is in solid solution in the
crystalline structure of the compound.
[0073] In some embodiments, M' is Fe and the solubility of M" in
the lattice can be improved if M" has an ionic radius, in
octahedral coordination, that is less than that of Fe.sup.2+.
Achieving solid solubility sufficient to increase the electronic
conductivity above 10.sup.-8 S/cm can require that processing
conditions (for example, temperature, atmosphere, starting
materials) allow M" to be stabilized in a particular valence state
that would provide an ionic radius less than that of Fe.sup.2+. In
some cases, for example, when solid solubility is achieved, the M"
ion may occupy the M1 site, or it may preferentially occupy the M2
site and cause Fe.sup.2+ or Fe.sup.3+, which would normally occupy
the M2 site, to occupy the M1 site.
[0074] Generalizing the M" solubility requirement to other olivines
of composition Li.sub.x-aM".sub.aM'PO.sub.4, M" typically has an
ionic radius that is less than the average ionic radius of ions M'
at the Li concentration x at which the compound is first
synthesized.
[0075] Electrochemical insertion and removal can later change the
valence distribution amongst the M' and M" ions. In some cases, M"
can be in the desired valence state and concentration by adding, to
the starting material, a salt of M" having the desired final
valence. However, the desired valence distribution amongst metals
M' and M" can be obtained by synthesizing or heat treating under
appropriate conditions of temperature and gas atmosphere. For
example, if M' is Fe, heat treatment should be conducted under
temperature and atmosphere conditions that preserve a predominantly
2+valence state, although some Fe.sup.3+ is allowable and can even
be beneficial for increasing conductivity.
[0076] In other cases, for example, for
Li.sub.x(M.sub.1-aM".sub.a)PO.sub.- 4 compositions, firing or heat
treating at 600.degree. C., can render the compositions conductive,
even if M", or M', is a divalent cation, such as Mg.sup.2+ or
Mn.sup.2+. In some cases, a Li.sub.3PO.sub.4 secondary phase can be
present. Thus, the olivine composition according to some
embodiments of the present invention may have a lithium deficiency
that can result in a Li.sub.x-aM".sub.aM'PO.sub.4 crystal
composition.
[0077] The possible dopants M" are not limited to those Groups of
the Periodic Table that were previously identified, rather, M" can
be any metal that satisfies the above requirements of size and
valence. Specifically, for compositions
Li.sub.x-aM'.sub.aM"PO.sub.4, where M' is Fe, M" may be Mg.sup.2+,
Mn.sup.2+, Fe.sup.3+, Al.sup.3+, Ce.sup.3+, Ti.sup.4+, Zr.sup.4+,
Hf.sup.4+, Nb.sup.5+, Ta.sup.5+, W.sup.4+, W.sup.6+, or
combinations thereof.
[0078] In another embodiment, the compounds of this invention can
be used as mixed protonic-electronic conductors for such
applications as fuel cell electrodes and gas-separation membranes.
Phospho-olivines, such as LiFePO.sub.4, can be doped to be highly
electronically conducting, while at the same time they can be
sufficiently lithium-ion conducting to provide good performance as
a lithium battery electrode. Electrochemical results show good
cycling and also demonstrate that the compound can be delithiated
while retaining good electronic conductivity. In some cases, the
olivine structure can be retained in the fully delithiated state.
That is, FePO.sub.4 has an olivine structure-type polymorph.
Therefore, a doped FePO.sub.4 may be protonatable to be a good
mixed protonic-electronic conductor, since phosphates are good
protonic conductors.
[0079] The conductive LiMPO.sub.4 compounds of this invention may
also be protonatable to form H.sub.xFePO.sub.4 conductors, where
0<x<1.1. Such compounds can be used as the electrode in a
proton-conducting fuel cell. Typically such an electrode can be
used with a proton-conducting and electronically insulating
electrolyte. Such compounds can also be used as a solid membrane
for separating hydrogen gas from gas mixtures. For example,
hydrogen can be dissociated to protons and electrons at one surface
of the membrane that is under a higher hydrogen partial pressure,
the protons would typically diffuse through the membrane to a
second surface at lower hydrogen partial pressure, and are
recombined with electrons to form hydrogen gas that would be
released to the atmosphere from the second surface.
[0080] In some embodiments, compounds of the invention have a
structure comprising a continuous network of transition-metal
filled anion polyhedral units. The polyhedral units may be
octahedrals or distorted octahedrals. The polyhedral units in the
structure can, for example, share at least one of vertices,
corners, edges, or faces with other polyhedral units. In some
cases, the polyhedral units share corners and edges with other
polyhedral units.
[0081] In some embodiments, the compound is an n-type conductor. In
others, the compound is a mixture of an n-type conductor and a
p-type conductor. In still others, the compound is a p-type
conductor.
[0082] In some embodiments, the compound is substantially fully
delithiated. The compound may be a p-type conductor when
substantially fully lithiated and an n-type conductor when
substantially fully delithiated. In some cases, the compound, upon
delithiation, undergoes phase-separation into a substantially
lithiated compound and a substantially delithiated compound, each
of which have an electronic conductivity of at least 10.sup.-6
S/cm.
[0083] The compounds of the present invention can be prepared
through a variety of techniques, including, for example,
solid-state reactions, co-precipitation from liquid solutions,
so-called sol-gel methods, or deposition from the vapor phase by
methods such as sputtering, laser ablation, electron-beam
evaporation, thermal evaporation, and chemical vapor deposition.
For large volume production, for example, such compositions can be
prepared by solid state reaction methods. For such reactions,
numerous possible starting materials are possible, the use of which
allows a general classification of the methods.
[0084] Salts of each of the metals are typically selected so that
they can react and decompose upon heating. Examples include salts
such as NH.sub.4H.sub.2PO.sub.4, Li.sub.2CO.sub.3, and
FeC.sub.2O.sub.4.2H.sub.2O for the main constituents (when, for
example, M" is Fe), and an alkoxide or metallorganic compound such
as Zr(OC.sub.2H.sub.4).sub.4,
Ti(OCH.sub.3).sub.4(CH.sub.3OH).sub.2, Nb(OC.sub.6H.sub.5).sub.5,
Ta(OCH.sub.3).sub.5, W(OC.sub.2H.sub.5).sub.6,
Al(OC.sub.2H.sub.5).sub.3, or Mg(OC.sub.2H.sub.5).sub.2 as the
source of the metal M". When using one or more of these materials
as the starting materials, gaseous species such as carbon oxides,
hydrogen, water, and ammonia can be generated and removed, if
necessary, during preparation.
[0085] The oxide Li.sub.2O, a divalent oxide of the metal M" (such
as FeO, MnO, or CoO), and P.sub.2O.sub.5 can be used as the source
of the main constituents. The metal M" is typically added as its
oxide in the preferred valence state, for example, as MgO,
TiO.sub.2, ZrO.sub.2, Fe.sub.2O.sub.3, Nb.sub.2O.sub.5,
Ta.sub.2O.sub.5, Al.sub.2O.sub.3, WO.sub.3, or WO.sub.6. When using
such exemplary starting materials, the compound can be crystallized
with substantially little or no evolution, or introduction, of
gaseous species. That is, the reaction of the starting can be
conducted in a closed-reaction system, typically without
substantial mass transport in, or out.
[0086] The present invention allows any mixture of starting
materials, some of which will yield a decomposition product, and
some of which will not. For example, a portion of the starting
materials can react to evolve or absorb gaseous species during
formation thereof. If Li.sub.2CO.sub.3 or LiOH.nH.sub.2O is used as
the lithium source, carbon oxide, or water, or both can be
generated during formation. Other constituents of the compound are
typically provided as oxide thereof, typically in the preferred
formal valence, (for example, as FeO, P.sub.2O.sub.5, and
Nb.sub.2O.sub.5), which typically do not evolve or absorb gaseous
species during the reaction. In other instances, starting materials
may be used that substantially comprise a closed system in which
there is little or no mass transport in or out of the reactants
during formation of the materials of the invention. One preferred
such reaction uses LiPO.sub.3 and FeO to form LiFePO.sub.4 as the
product. Adjustments to the relative amounts of the reactants, and
the addition of other constituents such as the dopants in the form
of oxides in which the cations have their preferred formal valence
state, are readily used in order to obtain compositions comprising
the materials of the invention.
[0087] The dopants M" can also be added by milling the starting
materials in milling media comprising the desired doping materials.
For example, zirconia or alumina milling balls or cylinders can be
used to introduce Zr or Al as the dopant. Milling equipment, such
as a milling container, made of such materials can also be used as
the source of dopant. The amount of dopant can be controlled by
monitoring the extent, intensity or duration or both, of milling
and controlling such until a predetermined dopant level is
achieved.
[0088] Further, milling media or containers can be used to add
carbon, for example, to the materials of the invention in small
quantities that can have a beneficial effect on the conductivity of
the material without substantially decreasing the energy density of
the material. The amount of carbon added in this instance is
preferably less than about 10 weight percent of the total mass of
the material, more preferably less than about 5 weight percent, and
still more preferably less than about 3 weight percent. Milling
containers or milling media that have such effect include those
made from polypropylene, polyethylene, polystyrene, and
fluoropolymers such as Teflon.RTM. (E.I du Pont de Nemours and
Company, Wilmington, Del.).
[0089] For Li.sub.x(M'.sub.1-aM".sub.a)PO.sub.4 compositions, a is
preferably less than about 0.05 and the compound is preferably heat
treated under various conditions.
[0090] A substantially reducing or inert gas atmosphere can be
used, for example, nitrogen, argon, nitrogen-hydrogen mixtures,
carbon dioxide-carbon monoxide mixtures, or mixtures of nitrogen
with oxygen or argon with oxygen. The oxygen partial pressure in
the gas mixture under the firing conditions applied to the
composition is typically less than about 10.sup.-3 atm, preferably
less than about 10.sup.-4 atm, more preferably less than about
10.sup.-5 atm, and still preferably less than about 10.sup.-6 atm.
When using salts that can decompose to yield gaseous products upon
heating, the compounds can be exposed to a first heat treatment to
decompose, in some cases, the salts leaving substantially only the
oxides of each metal, at a lower temperature than the final
crystallization heat treatment. For example, heat treatment at
350.degree. C. for ten hours in flowing nitrogen or argon is
typically sufficient to transform the starting materials if the
batch size is a few grams. A final heat treatment at a higher
temperature typically follows. In some cases, the material is not
heated to temperatures greater than about 800.degree. C. for longer
than about four hours. Preferably, the material is heated at less
than about 750.degree. C. but greater than about 500.degree. C.,
and is held at that temperature between four and twenty-four
hours.
[0091] For Li.sub.x-aM".sub.aM'PO.sub.4 compositions, a is
preferably less than 0.1 and the material can be heated to higher
temperatures and for longer times than described above, without
losing electronic conductivity. That is, these compositions can be
subjected to much wider ranges of heat treatment temperature and
time while still yielding high electronic conductivity. Various
heat treatments can also be used. For example, a substantially
reducing or inert gas atmosphere is used, for example, nitrogen,
argon, nitrogen-hydrogen mixtures, carbon dioxide-carbon monoxide
mixtures, or mixtures of nitrogen with oxygen or argon with oxygen.
The oxygen partial pressure in the gas mixture under the firing
conditions applied to the composition is typically less than about
10.sup.-4 atmosphere, preferably less than about 10.sup.-5 atm, and
still preferably less than about 10.sup.-6 atm. When using salts
that decompose to yield gaseous products upon heating, the
compounds may be exposed to a first heat treatment to decompose, in
some cases, the salts leaving substantially only the oxides of each
metal, at a lower temperature than the final crystallization heat
treatment. For example, a heat treatment at 350.degree. C. for ten
hours in flowing nitrogen or argon can be sufficient to transform
the starting materials if the batch size is a few grams. A final
heat treatment at a higher temperature typically follows. In some
cases, the material is heated to a temperature preferably greater
than 500.degree. C. and less than about 900.degree. C., still
preferably greater than about 550.degree. C. and less than about
800.degree. C., and is held at that temperature between four and
twenty-four hours.
[0092] While a detailed understanding of the conduction mechanism
in the materials of the present invention is not necessary to
define or to practice the invention, it is useful to elaborate a
possible mechanism that is consistent with the experimental
observations.
[0093] Measurements show that the highly conductive compositions
are typically p-type, not necessarily n-type, while the undoped
compositions can be n-type. This shows that acceptor defects can be
introduced by doping and heat treating as described herein. Having
a supervalent cation on the M1 site can introduce a donor on that
site. However, since the resulting materials are p-type, it is
believed that electronic compensation of a donor cation is not
necessarily the mechanism by which conductivity increases. Having
vacancies on the M2 iron sites, for ionic compensation of
supervalent cations on the M1 sites, or in order to
charge-compensate an excess of Fe.sup.3+ introduced on the M2
sites, can introduce acceptor states on the M2 sites. This is
analogous to having a subvalent dopant on the Fe site, and can
create an acceptor defect on the M2 sites. Having lithium
substituted for a cation of higher valence on the M2 sites can also
create acceptor defects on those sites. Having lithium deficiency
on the M1 site can also create acceptor defects on those sites.
[0094] Therefore, highly conductive p-type behavior can be obtained
when there are acceptor defects or ions on the M1 or M2 sites that
are not simultaneously charge-compensated by other solutes or
defects. However, for increased p-type conductivity to be obtained
in the compound, it is preferred that such acceptor defects form a
crystalline solid solution of the compound. For instance, in the
undoped and insulating compound LiFePO.sub.4, if upon delithiation
to an overall composition Li.sub.xFePO.sub.4 where x<1, the
compound forms two compositions or phases, LiFePO.sub.4 in which Fe
is substantially all in the ferrous (2+) state, and FePO.sub.4 in
which Fe is substantially all in the ferric (3+) state, then each
individual compound comprising the material is substantially
insulating, resulting in a whole material that is also
insulating.
[0095] Thus, in one embodiment, the present invention provides a
compound comprising a composition with a formula
A.sub.x(M'.sub.1-aM".sub.a).sub.y- (XD.sub.4).sub.z,
A.sub.x(M'.sub.1-aM).sub.y(DXD.sub.4).sub.z or
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z, having a
conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm. In
some embodiments, A is at least one of an alkali metal and
hydrogen, M' is a first-row transition metal, X is at least one of
phosphorus, sulfur, arsenic, molybdenum and tungsten, M" is any of
a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB,
VB, and VIB metal of the Periodic Table (catalog number S-18806,
published by Sargent-Welch, 1994), D is at least one of oxygen,
nitrogen, carbon, or a halogen, 0.0001<a.ltoreq.0.1, and x, y,
and z are greater than 0 and have values such that x, plus y(1-a)
times a formal valence or valences of M', plus ya times a formal
valence or valence of M", is equal to z times a formal valence of
the XD.sub.4, X.sub.2D.sub.7, or DXD.sub.4 group. In another
embodiment, the present invention provides a compound comprising a
composition with a formula
(A.sub.1-aM".sub.a).sub.xM'.sub.y(XD4).sub.z- ,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.1-aM".sub.a)M'.sub.y(X.sub.2D.sub.7).sub.z, having a
conductivity at 27.degree. C. of at least about 10.sup.-8 S/cm. In
some embodiments, A is at least one of an alkali metal and
hydrogen, M' is a first-row transition metal, X is at least one of
phosphorus, sulfur, arsenic, molybdenum and tungsten, M" is any of
a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB,
VB, and VIB metal, 0.0001<a.ltoreq.0.1, and x, y, and z are
greater than 0 and have values such that x, plus y(1-a) times a
formal valence or valences of M', plus ya times a formal valence or
valence of M", is equal to z times a formal valence of the
XD.sub.4, X.sub.2D.sub.7, or DXD.sub.4 group.
[0096] In yet another embodiment, the present invention provides a
fuel cell comprising a mixed proton conducting and electronically
conducting material having a formula
A.sub.x(M'.sub.1-aM".sub.a).sub.y(XD.sub.4).sub- .z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(DXD.sub.4).sub.z,
A.sub.x(M'.sub.1-aM".sub.a).sub.y(X.sub.2D.sub.7).sub.z,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(XD.sub.4).sub.z,
(A.sub.1-aM".sub.a).sub.xM'.sub.y(DXD.sub.4).sub.z, or
(A.sub.1-aM".sub.a).sub.xM'.sub.y(X.sub.2D.sub.7).sub.z. In the
compound, A is at least one of an alkali metal and hydrogen, M' is
a first-row transition metal, X is at least one of phosphorus,
sulfur, arsenic, molybdenum, and tungsten, M" any of a Group IIA,
IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB
metal, D is at least one of oxygen, nitrogen, carbon, or a halogen,
0.0001<a.ltoreq.0.1, and x, y, and z are greater than 0 and have
values such that x, plus y(1-a) times the formal valence or
valences of M', plus ya times the formal valence or valences of M",
is equal to z times the formal valence of the XD.sub.4,
X.sub.2D.sub.7 or DXD.sub.4 group.
[0097] In some embodiments of the invention, it may be preferable
for the compound to be substantially free of silicon. That is,
silicon is not present in amounts greater than trace amounts.
[0098] In a further embodiment, the present invention provides a
composition having a conductivity at about 27.degree. C. of at
least about 10.sup.-8 S/cm comprising primary crystallites with a
formula LiFePO.sub.4. The primary crystallites having an olivine
structure that can form at least a part of an interconnected porous
network.
[0099] In still another embodiment, the present invention provides
a method of providing electrical energy. The method comprises the
step of providing a battery having an electrode comprising a
compound having a conductivity at 27.degree. C. of at least about
10.sup.-8 S/cm and a capacity of at least about 80 mAh/g. The
method further comprises the step of charging the battery at a rate
that is greater than about C rate of the compound.
[0100] In still another embodiment, the present invention provides
a method of forming a compound. The methods include mixing an
alkali metal or hydrogen salt, a first-row transition metal salt, a
salt of at least one of phosphorus, sulfur, arsenic, silicon,
aluminum, boron, vanadium, molybdenum and tungsten, and a salt of
any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB,
IVB, VB, and VIB metal. The method further includes milling the
mixture and heat treating the mixture at a temperature between
300-900.degree. C. This method may be used to form any suitable
compound described herein.
[0101] In yet another embodiment, the present invention is directed
to a method of doping a material to form a conductive material. The
method comprises the steps of mixing powders of a lithium salt and
an iron oxide and adding an oxide of a dopant, the dopant having
the same valence state in the oxide as in the conductive material.
The method also comprises the step of heat treating the mixed
powders to form the doped conductive material.
[0102] And, in one embodiment, the present invention is directed to
a method of doping a material to form a conductive compound. The
method comprises the steps of selecting a starting material to be
doped, in conjunction with selection of milling equipment
comprising a dopant for doping the starting material at a
predetermined level of dopant and milling the starting material in
the milling equipment. The method further comprises the step of
recovering from the milling step a material suitable for forming a
conductive material comprising the starting material doped with the
dopant at the predetermined level.
[0103] Amongst other applications, the compounds, electrodes, and
battery cells of the invention are useful for high power, safe,
rechargeable lithium batteries for applications such as hybrid and
electric vehicles, back-up power, implantable medical devices, and
applications that currently use supercapacitor technology. The
combination of high electronic and ion transport at reduced
temperatures in these compounds also makes proton conducting
analogs useful as electrode materials for other electrochemical
applications such as low-temperature protonic fuel cell electrodes
or hydrogen gas separation membranes.
[0104] In some embodiments, electrodes are formed from any of the
compounds described herein. In some embodiments, though not all, it
may be preferable for the electrode materials to be lithium storage
compounds other than one of ordered or partially ordered rocksalt
crystal structure type, or spinel crystal structure type, or
vanadium oxide or manganese oxide. Examples of ordered or partially
ordered rocksalt crystal structure types include LiCoO2, LiNiO2,
LiMnO2, and their solid solutions. Examples of spinel crystal
structure type include LiMn2O4 and its solid solutions.
[0105] The electrode materials of the invention may have a variety
of material energy densities at different charging or discharging
rates. In one set of embodiments, the electrode has a material
energy density that, while charging or discharging at a rate
.gtoreq.800 mA per g of storage compound, is greater than 250
Wh/kg, or charging or discharging at a rate .gtoreq.1.5 A per g of
storage compound, is greater than 180 Wh/kg, or charging or
discharging at a rate .gtoreq.3 A per g of storage compound, is
greater than 40 Wh/kg, or charging or discharging at a rate
.gtoreq.4.5 A per g of storage compound, is greater than 10
Wh/kg.
[0106] In another set of embodiments, the electrode has a material
energy density that, while charging or discharging at a rate
.gtoreq.800 mA per g of storage compound, is greater than 350
Wh/kg, or charging or discharging at a rate .gtoreq.1.5 A per g of
storage compound, is greater than 270 Wh/kg, or charging or
discharging at a rate .gtoreq.3 A per g of storage compound, is
greater than 150 Wh/kg, or charging or discharging at a rate
.gtoreq.4.5 A per g of storage compound, is greater than 80 Wh/kg,
or charging or discharging at a rate .gtoreq.6 A per g of storage
compound, is greater than 35 Wh/kg, or charging or discharging at a
rate .gtoreq.7.5 A per g of storage compound, is greater than 50
Wh/kg, or charging or discharging at a rate .gtoreq.15 A per g of
storage compound, is greater than 10 Wh/kg.
[0107] In another set of embodiments, the electrode has a material
energy density that, while charging or discharging at a rate
.gtoreq.800 mA per g of storage compound, is greater than 390
Wh/kg, or charging or discharging at a rate .gtoreq.1.5 A per g of
storage compound, is greater than 350 Wh/kg, or charging or
discharging at a rate .gtoreq.3 A per g of storage compound, is
greater than 300 Wh/kg, or charging or discharging at a rate
.gtoreq.4.5 A per g of storage compound, is greater than 250 Wh/kg,
or charging or discharging at a rate .gtoreq.7.5 A per g of storage
compound, is greater than 150 Wh/kg, or charging or discharging at
a rate .gtoreq.11 A per g of storage compound, is greater than 50
Wh/kg, or charging or discharging at a rate .gtoreq.15 A per g of
storage compound, is greater than 30 Wh/kg.
[0108] Electrodes of the invention may have a variety of different
configurations depending on the application in which the electrode
is used. In some cases, the electrode may comprise a sheet or a
mesh coated or impregnated with the storage compound. In other
cases, the electrode comprises a metal foil coated one or both
sides with the storage compound.
[0109] The electrode may include different loading amounts of the
storage compound. For example, the electrode may include a loading
of at least 4 mg, 8 mg, 10 mg, 14 mg, or 20 mg per square
centimeter of projected area of the sheet or mesh.
[0110] The electrode may be a sheet or a mesh having a total
thickness of at least 20 micrometers, 40 micrometers, 60
micrometers, 80 micrometers, 100 micrometers, 150 micrometers, or
200 micrometers.
[0111] It should be understood that the electrodes of the invention
may have other configurations and structures than those described
herein.
[0112] FIG. 28 schematicaly illustrates a storage battery cell 10
according to one embodiment of the present invention. Storage
battery cell 10 includes a positive current collector 12 in contact
with a positive electrode 14. The storage battery cell further
includes a negative current collector 18 in contact with a negative
electrode 16. A separator 20 is positioned between the positive
electrode and the negative electrode. Either the positive or the
negative electrode (or both) may be comprised of any of the
compositions described herein.
[0113] Storage battery cells of the present invention may exhibit
different properties. For example, the cell may exhibit, upon
discharge, an energy of at least 0.25 Wh; in other cases, at least
1 Wh; in other cases, at least 5 Wh; in other cases, at least 10
Wh; in other cases, at least 20 Wh; in other cases, at least 30 Wh;
in other cases, at least 40 Wh; in other cases, at least 60 Wh;
and, in other cases, at least 100 Wh.
[0114] The storage battery cells may also exhibit a variety of
combinations of gravimetric energy and/or volumetric energy density
upon discharge. For example, the storage battery cell may exhibit a
discharge a gravimetric energy density of at least 30 Wh/kg or a
volumetric energy density of at least 100 Wh/liter; a gravimetric
energy density of at least 50 Wh/kg or a volumetric energy density
of at least 200 Wh/liter; a gravimetric energy density of at least
90 Wh/kg or a volumetric energy density of at least 300 Wh/liter; a
gravimetric power density of at least 500 W/kg or a volumetric
power density of at least 500 W/liter; a gravimetric power density
of at least 1000 W/kg or a volumetric power density of at least
1000 W/liter; a gravimetric power density of at least 2000 W/kg or
a volumetric power density of at least 2000 Wh/liter.
[0115] Storage battery cells of the invention may also exhibit a
variety of gravimetric energy density at different power densities.
For example, the storage cells may exhibit, upon discharge, a
gravimetric energy density of at least 30 Wh/kg at a power density
of at least 500 W/kg, or 20 Wh/kg at a power density of at least
1000 W/kg, or 10 Wh/kg at a power density of at least 1500 W/kg, or
5 Wh/kg at a power density of at least 2000 W/kg, or 2 Wh/kg at a
power density of at least 2500 W/kg, or 1 Wh/kg at a power density
of at least 3000 W/kg.
[0116] In another embodiment, the storage cells may exhibit, upon
discharge, a gravimetric energy density of 50 Wh/kg at a power
density of at least 500 W/kg, or 40 Wh/kg at a power density of at
least 1000 W/kg, or 20 Wh/kg at a power density of at least 2000
W/kg, or 10 Wh/kg at a power density of at least 3000 W/kg, or 4
Wh/kg at a power density of at least 4000 W/kg, or 1 Wh/kg at a
power density of at least 5000 W/kg.
[0117] In another embodiment, the storage cells may exhibit, upon
discharge, a gravimetric energy density of at least 80 Wh/kg at a
power density of at least 1000 W/kg, or 70 Wh/kg at a power density
of at least 2000 W/kg, or 60 Wh/kg at a power density of at least
3000 W/kg, or 55 Wh/kg at a power density of at least 4000 W/kg, or
50 Wh/kg at a power density of at least 5000 W/kg, or 30 Wh/kg at a
power density of at least 6000 W/kg, or 10 Wh/kg at a power density
of at least 8000 W/kg.
[0118] It should be understood that certain storage cells of the
invention may have a variety of different structures than those
described herein and exhibit different properties than those
described herein.
[0119] The present invention will be further illustrated through
the following examples, which are illustrative in nature and are
not intended to limit the scope of the invention.
EXAMPLE 1
Metal-Doped Compositions
[0120] This example demonstrates the preparation of compositions
having the formulation Li(Fe.sub.1-aM".sub.a)PO.sub.4, where M" is
Al, Ti, Zr, Mn, Nb, Ta, W, Mg, or Li. Specific compositions, heat
treatments, and results are listed in Tables 2 and 3, respectively.
It was found that the electronic conductivity increased only for
certain low concentrations of the metal additive or dopant. The
specific range of concentration providing a high electronic
conductivity (greater than about 10.sup.-5 S/cm) varied for each
dopant but was generally less than about 5 mole % of the Fe
concentration. In addition to having a low concentration of the
dopant, it was necessary to heat treat the material under
conditions such that high electronic conductivity was obtained.
These conditions included heat treatment in a non-oxidizing gas
atmosphere, including but not limited to argon, nitrogen, and
nitrogen-hydrogen mixtures. Moreover, the temperature of heat
treatment was less than about 800.degree. C. At 600.degree. C., the
firing time in the above described gas atmosphere was less than
about 100 hours.
[0121] Sample Preparation
[0122] Compositions as listed in Table 2 or otherwise described
herein were prepared as follows or as adjusted to suit the
particular composition by procedures illustrated for the following
compositions. The starting materials of this Example are listed in
Table 1.
1TABLE 1 Starting materials for a synthesis method for doped
LiFePO.sub.4 Theoretical *Analyzed Manufacturer/Purity content
content Compound (wt%) Element (wt %) (wt %) Li.sub.2CO.sub.3
Alfa-Aesar, 99.999 Li 18.8 18.9 FeC.sub.2O.sub.4.2H.sub.2O Aldrich,
99.99 Fe 31.0 30.7 NH.sub.4H.sub.2PO.sub.4 Alfa-Aesar, 99.998 P
26.9 27.2 * The metals content was analyzed using Direct Current
Plasma (DCP) emission spectroscopy following ASTM E1097.
[0123] The starting materials were weighed to high precision using
a laboratory balance. For example, Zr-doped LiFePO.sub.4 samples of
the following doping levels and batch sizes were prepared using the
following starting materials, wherein zirconium ethoxide served as
the source of the dopant:
2 5 mole % Zr, 1 mole% Zr 2 mole % Zr 5 g batch 2.5 g batch 2.5 g
batch NH.sub.4H.sub.2PO.sub.4 3.6465 g 1.7254 g 1.7254 g
Li.sub.2CO.sub.3 1.1171 g 0.554 g 0.554 g
FeC.sub.2O.sub.4.2H.sub.2O 5.4177 g 2.6715 g 2.6715 g
Zr(OC.sub.2H.sub.5).sub.4 0.4303 g 0.0407 g 0.0814 g
[0124] Similarly, 1 mole % and 2 mole % Ti-doped LiFePO.sub.4 were
prepared using the starting materials as above, except that
titanium methoxide, Ti(OCH.sub.3).sub.4(CH.sub.3OH).sub.2 was used
as the source of Ti (in place of the
Zr(OC.sub.2H.sub.5).sub.4):
3 1 mole % Ti 2 mole % Ti 2.5 g batch 2.5 g batch
NH.sub.4H.sub.2PO.sub.4 1.7254 g 1.7254 g Li.sub.2CO.sub.3 0.554 g
0.554 g FeC.sub.2O.sub.4.2H.sub.2O 2.6715 g 2.6715 g
Ti(OCH.sub.3).sub.4(CH.sub.3OH).sub.2 0.0354 g 0.0708 g
[0125] Undoped LiFePO.sub.4 samples were prepared from the same
materials except without the dopant salt. For the other samples,
with the dopants as listed in Table 2, an appropriate metal salt
was used. In particular, to prepare the Nb-doped samples, niobium
phenoxide, Nb(OC.sub.6H.sub.5).sub.5, was used as the dopant salt;
to prepare the Ta-doped samples, tantalum methoxide,
Ta(OCH.sub.3).sub.5, was used as the dopant salt; to prepare the
W-doped samples, tungsten ethoxide, W(OC.sub.2H.sub.5).sub.6, was
used as the dopant salt; to prepare the Al-doped sample, aluminum
ethoxide, Al(OC.sub.2H.sub.5).sub.3, was used as the dopant salt;
and to prepare the Mg-doped samples, magnesium ethoxide,
Mg(OC.sub.2H.sub.5).sub.2, was used as the dopant salt.
[0126] To prepare each sample, each of the components was weighed
in an argon-filled glove box. They were then removed from the glove
box and ball milled, using zirconia milling balls, in a
polypropylene jar for about twenty hours in acetone. The milled
mixture was dried at a temperature not exceeding 100.degree. C.,
and then ground with a mortar and pestle in the argon-filled glove
box. Each of the mixtures was then heat treated, given as "HT1"
through "HT7" under the conditions listed in Table 3. In each case,
a first heat treatment at 350.degree. C. for ten hours was
conducted in a flowing atmosphere of the specified gas. Each of the
powder samples was then ground, using a mortar and pestle, and
subjected to a second heat treatment at a higher temperature, in a
flowing atmosphere of the specified gas.
[0127] Conductivity Measurements
[0128] It is well-known that the electrical conductivity of solid
compounds is difficult to accurately measure from a finely divided
powder form of the compound. On the other hand, powders that have
been compacted and fired so as to achieve sintered contacts between
the powder particles, or have been partially or completely
densified, allow more accurate measurement of the conductivity of
the compound. For sintered pellets of reasonably high density, and
in which the particle contacts do not have a higher specific
resistance, the conductivity of the pellet is reduced from that of
the compound itself in approximately linear proportion to the
amount of porosity that is present. For example, a pellet that has
10% porosity may be judged to have about 90% of the conductivity of
the compound. In order to measure the conductivity when samples
were prepared in a powder form, pellets were pressed out of the
heat treated powder sample prior to the second heat treatment, and
placed in alumina crucibles during the second heat treatment so
that the powders and sintered pellets were heat treated together.
The density of the fired pellets were from about 60% to about 95%
of the crystal density, depending on composition and heat
treatment.
[0129] In order to measure electrical conductivity, 2-point and
4-point (van der Pauw, vdP) conductivity measurements were
performed according to known conventional procedures. Because metal
contacts that are blocking to lithium ions and conductive to
electrons were used, the resulting conductivities are understood to
reflect the electronic conductivity of the compound. The room
temperature conductivities of several of the doped samples are
listed in Table 2.
[0130] X-ray Diffraction, Electron Microscopy, Specific Surface
Area Measurement, and Chemical Analysis
[0131] Several methods were used to determine the crystalline
phase, extent of crystallization, powder particle size and
morphology, specific surface area of the powder, and the location
of dopants. Samples were evaluated by x-ray diffraction after heat
treatment to determine the crystalline structure as well as to
determine if there was a detectable secondary phase. In some cases,
some of the powder samples were examined at higher resolution by
transmission electron microscopy (TEM) and/or scanning transmission
electron microscopy (STEM) to determine whether secondary phases
were present, whether a surface coating of another phase were
present, and to measure the concentration of the dopant metal
within the crystalline grains of the LiFePO.sub.4 phase. This
allowed a determination of whether the metal dopant, at the added
concentration and heat treatment, was soluble or had exceeded its
solubility limit in the LiFePO.sub.4 phase. It was also possible to
determine whether the particles of crystallized compound had a
surface coating of another material. In some cases, the composition
of the powders or pellets were determined using direct current
plasma (DCP) emission spectroscopy according to ASTM ASTM E1097, or
combustion IR detection according to ASTM E1019.
[0132] In the samples listed in Table 2, the first numeral
indicates the dopant, the second the concentration, and the third,
the heat treatment. For example, sample 3c1 refers to a Ti-doped
sample of 0.1 mole % concentration subjected to the heat treatment
HT1. Where the concentration of dopant is given herein in mole
percent, it refers to the relative molar fraction, Ti/(Ti+Fe)
multiplied by 100.
4TABLE 2 Results for Undoped and Doped Lithium Iron Phosphates Room
Temperature Conductivity Heat (S/cm) XRD/TEM/ Minor Composition
Treat- van der STEM phases (Sample) ment 2-point Pauw observations
(by XRD) 1. Undoped (1a1) HT1 <10.sup.-6 -- Single phase None
detected LiFePO.sub.4 olivine (1b2) HT2 <10.sup.-6 -- Single
phase None detected LiFePO.sub.4 olivine (1c3) HT3 <10.sup.-6 --
Single phase None detected LiFePO.sub.4 olivine (1d6) HT6 2.2
.times. 10.sup.-9.dagger. -- Single phase None detected
LiFePO.sub.4 olivine (1e6) HT6 3.74 .times. 10.sup.-10.dagger-dbl.
-- Single phase None detected LiFePO.sub.4 olivine (1f7) HT7 2.22
.times. 10.sup.-9.dagger. -- -- -- LiFePO.sub.4 (1g8) HT8 1.8
.times. 10.sup.-10 -- Multi-phase Li.sub.3PO.sub.4, Fe.sub.3P
LiFePO.sub.4 2. Aluminum (2a1) HT1 8.2 .times. 10.sup.-5 -- Dopant
soluble None detected Li(Al.sub..002Fe.sub..998)PO.sub.4 (2b6) HT6
.about.10.sup.-3 -- Dopant soluble None detected
(Li.sub..99Al.sub..01) FePO.sub.4 3. Titanium (3c5) HT5
<10.sup.-5 -- Dopant soluble None detected
Li(Ti.sub..001Fe.sub..999)PO.sub.4 (3d1) HT1 1.7 .times. 10-4 --
Exceeds Not identified Li(Ti.sub..002Fe.sub..998)PO.sub.4
solubility (3e1) HTI 2.0 .times. 10.sup.-4 -- Exceeds
Li.sub.3PO.sub.4 Li(Ti.sub..01Fe.sub..99)PO.sub.4 solubility (3e2)
HT2 1.9 .times. 10.sup.-4 -- Exceeds Li.sub.3PO.sub.4
Li(Ti.sub..01Fe.sub..99)PO.sub.4 solubility (3e3) HT3 <10.sup.-6
-- Exceeds Not identified Li(Ti.sub..002Fe.sub..998)- PO.sub.4
solubility (3f2) HT2 1.4 .times. 10.sup.-6 -- Exceeds Not
identified Li(Ti.sub..02Fe.sub..98)PO.sub.4 solubility (3g6) HT6
1.3 .times. 10.sup.-3.dagger-dbl. -- Dopant soluble None detected
(Li.sub..99Ti.sub..01)FePO.sub.4 (3g7) HT7 2.3 .times.
10.sup.-2.dagger-dbl. -- Exceeds Li.sub.3PO.sub.4, Fe.sub.2P
(Li.sub..99Ti.sub..01)FePO.sub.4 solubility 4. Zirconium (4a1) HT1
5.0 .times. 10.sup.-5 -- Dopant soluble None detected
Li(Zr.sub..002Fe.sub..998)PO.sub.4 (4b1) HT1 3.7 .times. 10.sup.-4
-- Exceeds Li.sub.3PO.sub.4 Li(Zr.sub..01Fe.sub..99)PO.s- ub.4
solubility (4b2) HT2 4.5 .times. 10.sup.-5 -- Exceeds
Li.sub.3PO.sub.4 Li(Zr.sub..01Fe.sub..99)PO.sub.4 solubility (4b3)
HT3 <10.6 -- Exceeds Not identified
Li(Zr.sub..01Fe.sub..99)PO.sub.4 solubility (4c2) HT2 18 .times.
10.sup.-4 -- Exceeds Li.sub.2ZrO.sub.3
Li(Zr.sub..02Fe.sub..98)PO.sub.4 solubility (4d2) HT2
.about.10.sup.-5 -- Exceeds Li.sub.2ZrO.sub.3
Li(Zr.sub..05Fe.sub..95)PO.sub.4 solubility (4e1) HT1
.about.10.sup.-4 -- Dopant soluble None detected
Li(Zr.sub..99Fe.sub..01)PO.sub.4 (4e2) HT2 1.6 .times. 10.sup.-2 --
Exceeds Li.sub.3PO.sub.4, Fe.sub.2P Li(Zr.sub..01Fe.sub..99)PO.-
sub.4 solubility 5. Niobium (5b1) HT1 1.3 .times. 10.sup.-4 --
Dopant soluble None detected Li(Nb.sub..001Fe.sub..99- 9)PO.sub.4
(5c1) HT1 5.8 .times. 10.sup.-4 -- Dopant soluble None detected
Li(Nb.sub..002Fe.sub..998)PO.sub.4 (5c4) HT4 <10.sup.-6 -- -- --
Li(Nb.sub..002Fe.sub..998)PO.sub.4 (5e6) HT6 1.1 .times. 10.sup.-3
-- Dopant soluble None detected (Li.sub..998Nb.sub..002)FePO.sub.4
(5e7) HT7 1.1 .times. 10.sup.-2.dagger-dbl. -- Dopant soluble None
detected (Li.sub..998Nb.sub..002)FePO.sub.4 (5f6) HT6 4.1 .times.
10.sup.-2 -- Dopant soluble None detected (Li.sub..995Nb.sub..005)-
FePO.sub.4 (5g6) HT6 2.2 .times. 10.sup.-2 2.73 .times. 10.sup.-2
Dopant soluble None detected (Li.sub..99Nb.sub..01)FePO.sub.4 (5g7)
HT7 4.3 .times. 10.sup.-2.dagger-dbl. -- Exceeds Li.sub.3PO.sub.4,
Fe.sub.2P (Li.sub..99Nb.sub..01)FePO.sub.4 solubility (5h6) HT6 2.8
.times. 10.sup.-3 -- Exceeds Fe.sub.2P
(Li.sub..98Nb.sub..02)FePO.sub.4 solubility (5i6) HT6
.about.10.sup.-6 -- Exceeds Fe.sub.2P (Li.sub..96Nb.sub..04)FePO.s-
ub.4 solubility 6. Tantalum (6a1) HT1 3.0 .times. 10.sup.-5 --
Dopant soluble None detected Li(Ta.sub..002Fe.sub..9- 98)PO.sub.4
7. Tungsten (7a1) HT1 1.5 .times. 10.sup.-4 -- Dopant soluble None
detected Li(W.sub..002Fe.sub..998)PO.sub.4 8. Magnesium (8a1) HT1
.about.10.sup.-4 -- Dopant soluble None detected
Li(Mg.sub..002Fe.sub..998)PO.sub.4 (8b6) HT6 6.8 .times.
10.sup.-4.dagger-dbl. -- Dopant soluble None detected
(Li.sub..99Mg.sub..01)FePO.sub.4 (8b7) HT7 2.4 .times.
10.sup.-2.dagger-dbl. -- Exceeds Li.sub.3PO.sub.4, Fe.sub.2P
(Li.sub..99Mg.sub..01)FePO.sub.4 solubility (8b8) HT8 3.8 .times.
10.sup.-3.dagger-dbl. -- Exceeds Li.sub.3PO.sub.4, Fe.sub.2P
(Li.sub..99Mg.sub..01)FePO.sub.4 solubility 9. Manganese (2+) (9a1)
HT1 .about.10.sup.-4 -- Dopant soluble None detected
Li(Mn.sub..002Fe.sub..998)PO.sub.4 10. Iron (2+) (10a6) HT6
<10.sup.-6 -- Exceeds Li.sub.3PO.sub.4, Fe,
(Li.sub..99Fe.sub..01)FePO.sub.4 solubility 11. Iron (3+) (11a6)
HT6 3.3 .times. 10.sup.-2 4.1 .times. 10.sup.-2 Exceeds
Li.sub.3PO.sub.4, Fe, (Li.sub..99Fe.sub..01)FePO.sub.4 solubility
12. Lithium (12a6) HT6 <10 -- Exceeds Li.sub.3PO.sub.4, Fe,
Li(Fe.sub.0.99Li.sub..01)PO.sub.4 solubility .dagger.measurement by
AC Impedance Spectroscopy .dagger-dbl.measurement by two point
method, using sputtered Au electrodes.
[0133]
5TABLE 3 Heat Treatment Conditions Heat Conditions Treatment (all
gases at 1 atm total pressure) HT1 350.degree. C., 10 hours, Ar
600.degree. C., 24 hours, Ar -- HT2 350.degree. C., 10 hours,
N.sub.2 600.degree. C., 24 hours, N.sub.2 -- HT3 350.degree. C., 10
hours, N.sub.2 800.degree. C., 24 hours, N.sub.2 -- HT4 350.degree.
C., 10 hours, N.sub.2 800.degree. C., 24 hours, N.sub.2 -- HT5
350.degree. C., 10 hours, Ar 600.degree. C., 24 hours, Ar
600.degree. C., 76 hours, Ar HT6 350.degree. C., 10 hours, Ar
700.degree. C., 20 hours, Ar -- HT7 350.degree. C., 10 hours, Ar
850.degree. C., 20 hours, Ar -- HT8 350.degree. C., 10 hours, Ar
800.degree. C., 15 hours, Ar --
[0134] Results
[0135] X-ray diffraction showed that after the 350.degree. C. heat
treatment, the powders of this example were poorly crystallized and
not of a single major crystalline phase. After the second, higher
temperature heat treatment, all samples subjected to XRD showed
peaks associated with the olivine structure. The relative intensity
of X-ray peaks showed that the olivine phase was the major
crystalline phase. Visual observation of the heat treated powders
and pellets proved to be a reliable indication of whether or not
increased electronic conductivity had been obtained. While the
undoped LiFePO.sub.4 was light to medium gray, the conductive doped
powders and sintered pellets, regardless of specific dopant,
concentration, or heat treatment, were colored black. Conductive
sintered pellets were also easily distinguished from insulating
pellets with a simple ohmmeter measurement using two steel probes
placed 0.5-1 cm apart. Insulating compositions had resistances too
great to measure (being greater than the instrument limit of 200
M.OMEGA.), while conductive samples had resistances of typically 30
k.OMEGA. to 300 k.OMEGA..
[0136] The results in Table 2 show that heat treating undoped
LiFePO.sub.4 was not effective in producing an acceptable
conductive material; each of the conductivities of sintered pellets
was less than about 10.sup.-6 S/cm. The undoped compound was also
found to have a very narrow range of cation nonstoichiometry, with
as little as 1% deficiency of the ferrous iron oxalate resulting in
a detectable amount of Li.sub.3PO.sub.4 phase.
[0137] In contrast, for the dopants listed, at low concentrations,
it was possible to produce a sample having a room temperature
conductivity greater than about 10.sup.-5 S/cm. These conductivity
values exceed known values for the positive electrode compound
LiMn.sub.2O.sub.4. Further, Al, Ti, Zr, Nb, W, Mg, Mn, and
Fe(3+)-doped samples could be produced with a conductivity greater
than 10.sup.-4 S/cm.
[0138] Electron microscopy showed that the highly electronically
conductive samples did not have a surface coating or other form of
an additional conductive phase. A typical image is shown in FIG. 1,
which is a copy of a TEM image of a 0.01% Ti-doped sample.
[0139] The figures show that the doped compositions of
LiFePO.sub.4, synthesized in non-oxidizing or inert atmosphere at
temperatures below about 800.degree. C., had increased electronic
conductivity compared to the undoped LiFePO.sub.4 compositions,
thus making them useful as lithium storage electrodes especially at
practical charge/discharge rates. At the low doping levels used,
the doping does not limit the ability of the material to store
lithium at a high voltage (about 3.5V relative to lithium metal) or
achieve a high lithium storage capacity.
[0140] The results also showed that too high a heat treatment
temperature, and/or too long a heat treatment period, can result in
insulating materials. As a specific comparison, the Ti-doped
sample, sample 3e3, which was heat treated at 800.degree. C. for
twenty-four hours, was insulating (less than 10.sup.-6 S/cm)
whereas a similar 1% Ti-doped composition, samples 3e1 and 3e2,
which were heat treated at 600.degree. C. for twenty-four hours,
were highly conductive (2.times.10.sup.4 and 1.9.times.10.sup.-4
S/cm). The insulating sample 3e3 was examined using an STEM, which
showed that, unlike the conductive samples, the amount of Ti in
solid solution in the parent phase was not detectable (by
energy-dispersive x-ray analysis). Titanium appeared to aggregate
as a second phase, as shown in FIG. 2 (right side images). Thus, a
high temperature heat treatment can cause the dopant to become
insoluble. Similarly, the Zr-doped sample, 4b3, was also heat
treated at 800.degree. C. for twenty-four hours, and was insulating
(less than 10.sup.-6 S/cm). A similar 1% Zr-doped composition,
which was heat treated at 600.degree. C. for twenty-four hours in
argon or nitrogen, 4b1 and 4b2, was conductive. The Nb-doped
sample, 5c4, was heat treated at 800.degree. C. for twenty-four
hours and was found to be insulating, whereas a similar 0.2%
Nb-doped composition that was heat treated at 600.degree. C. for
twenty-four hours in argon or nitrogen, 5a1 and 5b1, was highly
conductive. Copies of STEM images of the Nb-doped samples are shown
in FIG. 3. Notably, Nb appears to have a higher solubility limit
than either Ti or Zr.
[0141] Moreover, even at a lower heat treatment temperature
(600.degree. C.), too long a heat treatment time can convert a
conductive composition to insulating composition. For example,
sample 3c5 was initially heat treated at HT1. A pellet was then
pressed and heat treated an additional 76 hours, in argon, and was
found to be less conductive relative to sample 3c1, which had a
similar composition but was not heat treated an additional 76
hours.
[0142] Further, the results also showed that there is a dopant
limit and that too much dopant can result in an insulating
composition. For example, a 2 mole % Ti-doped composition, 3f2, is
less conductive than a 1 mole % Ti-doped composition, 3e2. Notably,
a 2 mole % Zr-doped composition, 4c2, is still relatively
conductive, if not more conductive, compared to a 1 mole % Zr-doped
composition, 4b2. However, increasing the Zr concentration to 5
mole %, as in sample 4d2, reduced the conductivity. X-ray
diffraction analysis showed that the 5 mole % Zr-doped sample had a
small amount of secondary phase, which appeared to be
Li.sub.2ZrO.sub.3. In contrast, the 2 mole % Zr-doped sample had
peaks, corresponding to the latter phase, which were negligible, as
shown in FIG. 4.
[0143] Further, the results showed that the powders prepared were
free of coatings of carbon or other conductive additive phases. TEM
and STEM showed that the powders of Examples 1 and 2 typically
contained a small fraction of unreacted precursors in addition to
the majority phase of the olivine structure. However, TEM images at
resolution levels high enough to image the lattice planes of the
olivine phase, an example of which is shown in FIG. 5, showed that
the surfaces of the particles were not coated with another
distinguishable phase of material. Thus the increased conductivity
of the conductive powders of this Example was obtained in the
absence of a continuous phase of a conductive additive.
[0144] Other polyanion compounds, aside from those having the
olivine structure, such as those of the NASICON VOPO.sub.4,
LiFe(P.sub.2O.sub.7) or Fe.sub.4(P.sub.2O.sub.7).sub.3 structures,
can be similarly doped and synthesized to achieve high electronic
conductivity. Further, based on the results obtained using Mg as a
dopant, it is believed that other Group IIA alkaline earth metals,
such as Be, Ca, Sr, and Ba, should have similar effects. Based on
the results obtained using Ti and Zr, which are Group IVA elements,
it is believed that other Group IVA elements, such as Hf, should
have similar effects. Based on the results obtained using Nb and
Ta, which are Group VA elements, it is believed that other Group VA
elements, such as V, should have similar effects. Based on the
results obtained using W, which is a Group VIA element, it is
understood that other Group VIA elements, such as Cr and Mo, should
have similar effects. Based on the results obtained using Al, it is
believed that other Group IIIB elements, such as B, Ga, and In,
should have similar effects.
EXAMPLE 2
Lithium Deficient and Substituted Compositions
[0145] Several compositions were prepared with an overall
composition of the formula Li.sub.1-aM".sub.aFePO.sub.4, included
in Table 2. The starting materials and synthesis procedure of
Example 1 were used, with the exception that both plastic and
porcelain milling containers were used with the zirconia milling
media. Because the abrasion of polymeric milling containers and
milling media can be a source of carbon, the porcelain containers
were used to compare results with and without this potential carbon
source.
[0146] As shown in Table 2 and also in Table 4, the doped samples
of this doping formulation generally had higher conductivity than
those of Example 1, with room-temperature conductivities of as much
as about 4.times.10.sup.-2 S/cm being measured by a two-point
method (samples 5f6 and 5 g7). Highly conductive samples were
obtained using either plastic or porcelain milling containers,
showing that excess carbon added from the milling container is not
necessary to achieve such conductivities. The results show that
introducing Li/metal cation nonstoichiometry can promote Li
deficiency, relative to the ideal LiMPO.sub.4 stoichiometry, which,
combined with doping with selected metals, can increase electronic
conductivity. Also, higher temperature heat treatments, such as HT6
and HT7, can be used with these lithium-deficient cation
stoichiometry compositions without losing electronic conductivity
or exsolving the dopant, in comparison to the
LiFe.sub.1-aM".sub.aPO.sub.4 compositions (Example 1). STEM
observations showed that compositions exhibiting a detectable
concentration of the added dopant in the crystalline LiFePO.sub.4
grains were conductive.
[0147] Compositions Li.sub.1-xM.sub.xFePO.sub.4, that, while not
being bound by any particular crystal chemical interpretation, have
a formulation that allows substitution onto the M1 sites by a
cation supervalent to Li.sup.+, exhibited higher solubility for
several dopants (Mg.sup.2+, Al.sup.3+, Ti.sup.4+, Nb.sup.5+, and
W.sup.6+) than did compositions LiFe.sub.1-xM.sub.xPO.sub.4. FIG. 6
compares the X-ray diffraction patterns for several 1 mol % doped
powders of each cation stoichiometry; in each case the
lithium-deficient stoichiometry (FIG. 6a) exhibits no detectable
impurity phases. By contrast, samples with the same dopants and
concentrations in the iron-deficient stoichometry showed detectable
precipitation of Li.sub.3PO.sub.4 by XRD (FIG. 6b) and impurity
phases enriched in the dopant, using electron microscopy. FIG. 7
shows an example of the first stoichiometry,
Li.sub.0.99Nb.sub.0.01FePO.s- ub.4, in which elemental mapping
shows a uniform distribution of the Nb dopant. The amount of the
dopant in solid solution may be less than the total amount of
dopant added to the sample. For example, in the
Li.sub.1-aNb.sub.aFePO.sub.4 compositions, heat treated at
850.degree. C., a concentration x about 0.0023 was detected in
solid solution for an overall composition a about 0.01. This shows
that the solid solubility was limited to about a=0.0023 at
850.degree. C. Nonetheless, compositions with a values, both
greater than or less than 0.0023, were made conductive. In the
Li.sub.x(Fe.sub.1-aM".sub.a)PO.sub.4 compositions, samples
processed at 600.degree. C. were conductive while those processed
at 700.degree. C. and higher were not. Correspondingly, the samples
processed at 600.degree. C. had detectable dopants in solid
solution when examined by STEM, while those processed at
700.degree. C. did not.
[0148] The observed results that the increase in conductivity is
not directly proportional to dopant concentration is consistent
with a limited dopant solubility in some cases. That is, for those
dopants that increased electronic conductivity, there was a large
increase in conductivity at lower doping levels and weaker
conductivity-concentration dependence at slightly higher dopant
levels. For example, in the case of LiFe.sub.1-aM".sub.aPO.sub.4,
the greater than 100 times increase in conductivity, compared to
the undoped material, at dopant concentrations as low as 0.02% (for
M"=Ti, Nb, and Mg), is followed by much smaller changes in
conductivity with further increases in dopant concentration. For
compositions Li.sub.1-aM".sub.aFePO.sub.4, the electronic
conductivity is firstly higher overall by at least about an order
of magnitude than for any of the LiFe.sub.1-aM".sub.aPO.sub.4
compositions. Compared to the undoped material, the increase in
conductivity is significant, greater by a factor of more than
10.sup.7 times, with a doping level as low as 0.2% (Nb-doped).
However, further doping increases the conductivity only
modestly.
[0149] Materials were also synthesized that contained an excess of
Fe, typically in the form of an Fe.sup.2+ or Fe.sup.3+ salt, as
shown in Table 2. While an excess of either Fe.sup.2+ or Fe.sup.3+
can be substituted into the composition
Li.sub.1-aM".sub.aFePO.sub.4, as with the other dopants M", a
certain concentration must be in solid solution (i.e., form part of
the crystal lattice) for the conductivity to be increased
substantially, since this determines the electronic carrier
concentration. The results with Fe.sup.2+ and Fe.sup.3+ doping are
consistent with the experiments using other dopants M" that show
that when conductivity increased, the dopant in question was found
to be in solid solution (either through STEM measurements of dopant
distribution in the crystallites or by the appearance/absence of
impurity phases by STEM or XRD).
[0150] Further, it is believed that the solubility of dopants M" is
a function of ion size. With the exception of Mn.sup.2+, all of the
dopants that can be effective as M' dopants have an ionic radius,
in octahedral coordination, that was less than that of Fe.sup.2+.
This is supported by the following ionic radii values, taken from
the tabulation by Shannon (1976):
[0151] R(Fe.sup.2+)=0.78 A R(Li.sup.+)=0.76 A
[0152] R(Fe.sup.3+)=0.65 A R(Mg.sup.2+)=0.72 A R(Mn.sup.2+)=0.83 A
R(Ti.sup.4+)=0.61 A
[0153] R(Zr.sup.4+)=0.72 A R(Nb.sup.5+)=0.64 A R(Ta.sup.5+)=0.64 A
R(W.sup.6+)=0.60 A
[0154] R(Al.sup.3+)=0.54 A
[0155] The temperature dependence of conductivity in the materials
of the invention was measured using 2-point and 4-point electrical
conductivity measurements of fired pellets pressed from powder
samples prepared according to Examples 1 and 2. Both undoped and
doped compositions were measured. In addition, ac (impedance
spectroscopy) measurements were made on pellets prepared from
undoped powder. The temperature dependence of electrical
conductivity is shown in FIGS. 8 and 9 as a plot of log.sub.10
conductivity against 1000/T(K). It is seen that the doped
compositions can have more than 10.sup.7 greater conductivity than
an undoped sample. While both types exhibited increasing
conductivity with increasing temperature, indicating semiconducting
behavior, the doped materials had much shallower temperature
dependence. An activation energy in the range of 25-75 meV was
determined for the highly conductive doped samples, which is
reasonable for ionization of shallow acceptors or donors, while an
activation energy of about 500 meV was observed for the undoped
sample. The high conductivity of the doped samples is maintained,
with little temperature dependence, over the -20.degree. C. to
+150.degree. C. temperature range of interest for many battery
applications. Near room temperature, for example between 21C to
27C, the variation of electronic conductivity with temperature is
minor, such that where a temperature within this range is referred
to herein, it is understood that a range of temperatures around any
particular value is included.
[0156] The highly conductive samples were also subjected to a
Seebeck coefficient measurement. Platinum leads were attached to
two ends of a sintered sample, whereupon one end was heated to a
higher temperature than the other end, and the induced voltage was
measured. The heated end was found to be at a negative potential
relative to the cold end, exhibiting easily measured and
significant potential values of -0.1 mV to -0.3 mV. This shows that
the conductive LiFePO.sub.4 compositions were p-type conductors. An
undoped LiFePO.sub.4 composition subjected to the same measurement
was found to be n-type.
[0157] In some cases, the electrical conductivity of the samples
was measured using a four-point microcontact method in order to
determine the conductivity of individual crystalline grains. For
these measurements, densely sintered pellets with an average grain
size of about 10 micrometers were cut and polished. A co-linear
array of microcontacts were used. Current probes were placed about
100 micrometers apart on the polished surface, while voltage probes
were placed about 10 micrometers apart. FIG. 10 shows three samples
whose conductivities at the microscopic scale were measured, two
being 1% Nb-doped conductive compositions sintered at 850C and 900C
respectively, and one being an undoped composition sintered at
900C. Combustion IR detection showed that all three samples had low
carbon content, less than 0.5 wt %. The gray phase in FIG. 10 is
the olivine phase, the black contrast features are porosity, and
the bright contrast particles are iron phosphide phase. FIG. 11
shows the microcontact measurement geometry, in which it is seen
that the inner voltage contacts are about 10 micrometers apart, or
about the same separation as individual grains in the samples of
FIG. 10. Thus the voltage contacts typically span one grain or one
grain boundary. The microcontact array was placed in 12 to 15
separate locations on each sample, and the current-voltage
relationship was measured at teach point over a range of currents
in a room-temperature laboratory. FIG. 12 shows histograms of the
conductivity obtained from the measurements, in which each bar
represents one location of the microcontact array. It is seen that
firstly, within each sample the conductivity has a similar value
from place to place showing relatively uniform conductivity across
a sample. Secondly, the conductivity of the doped samples is of
about the same magnitude as measured by two-point and four-point
measurements across entire sintered pellets, and is several orders
of magnitude greater than the conductivity of the undoped
sample.
[0158] TEM observations were made of the powders of Example 2. FIG.
13 shows copies of TEM images of powders doped with 1% Nb or 1% Zr.
It is seen that the average size of individual crystallites is less
than about 100 nm in the Nb-doped sample, less than about 50 nm in
the Zr-doped sample, and that the powder has an aggregated
morphology. Energy-dispersive X-ray analysis was conducted to
determine the location of residual carbon, typically present at a
level determined by combustion IR analysis to be between 0.2 and
2.5 wt % depending on the firing conditions. FIG. 14 shows TEM
images and corresponding chemical analyses of regions in a 1% Nb
doped sample fired at 600C and that was analysed to have about 2.4%
residual carbon. This sample of relatively high residual carbon
content compared to others of Example 2 was selected for TEM in
order to determine if a carbon coating on the particles as
practiced in prior art was present. FIG. 14 shows a particle of
unreacted precursor, present in small amounts in the sample, in
which carbon is found at an enriched level. In the other regions,
containing the olivine phase, no carbon is detected. FIGS. 15 and
16 show high resolution TEM images of olivine phase particles, in
which lattice fringes are imaged. No continuous surface phase of
carbon or other separate conductive compound was found. Thus it is
seen that the fine particle size and increased conductivity of
these samples is observed in samples without a significant amount
of free carbon.
[0159] Surface area measurements are another well-known measure of
effective particle size. The specific surface area was measured,
using the BET method, of doped and undoped samples heat treated
under several conditions. Table 4 shows results for several powder
samples. It is observed that the undoped powders have a specific
surface area that is typically less than about 10 m.sup.2/g for
heat treatment temperatures of 600.degree. C. or greater. These are
heat treatment conditions sufficient to provide a nearly completely
crystallized powder. However, the doped compositions have much
higher surface area, typically greater than 40 m.sup.2/g for 1%
Zr-doped powder fired at 600C, and greater than 30 m.sup.2/g for 1%
Nb-doped powder fired at 600C. In the doped samples the powder is
also nearly completely crystallized after firing at these
temperatures although a small quantity of incompletely crystallized
precursor to the olivine phase remains. Other powders doped with
0.2-1 mole % of dopants such as Al, Mg, and Ti also had specific
surface areas of 35 to 42 m.sup.2/g after firing at 600C. At higher
firing temperatures of 700 to 800.degree. C. the specific surface
area of the doped samples remains higher than of the undoped
samples. Having a crystal density of 3.6 g/cm.sup.3, the diameter
of monosized spheres of the compound having an equivalent specific
surface area (i.e., the equivalent spherical particle size) of 40
m.sup.2/g is 21 nm, of 30 m.sup.2/g is 28 nm, of 29 m.sup.2/g is 42
nm, of 15 m.sup.2/g is 56 nm, of 10 m.sup.2/g is 83 nm, of 5
m.sup.2/g is 167 nm, and of 1 m.sup.2/g is 833 nm. Thus it is seen
that the doping methods of the present example provide for complete
or nearly complete crystallization of the olivine structure
compound while also providing for a high specific surface area,
higher than that of the undoped compound under identical processing
and firing conditions.
6TABLE 4 Compositions, Firing Conditions, and Specific Surface
Areas of Insulating and Conductive Samples BET area Composition
Temp. (.degree. C.) Container (m.sup.2/g) Conductivity Color
LiFePO.sub.4 600 Plastic bottle 9.5 insulating Gray 700 Porcelain
jar 3.9 insulating Gray 800 Porcelain jar .about.1 insulating Light
Gray LiFe.sub..099Zr.sub.0.01PO.sub.4 600 Porcelain jar 43.2
conductive Black 600 Porcelain jar 41.8 conductive Black 700
Porcelain jar 26.4 conductive Black 750 Porcelain jar 11.6
conductive Dark gray LiFe.sub.0.99Nb.sub.0.01PO.sub.4 600 Porcelain
jar 34.7 conductive Black 800 P Porcelain jar 15.3 conductive
Black
[0160] Without being bound by any particular interpretation, these
results show that conductivities, higher than those obtained using
the method and compositions of Example 1, can be obtained in a
composition that is deficient in the alkali ion and excess in the
other metals that would normally occupy octahedral sites in a
LiFePO.sub.4 structure. As mentioned, the results show that the
solubility of the metal, M", was higher when the composition was
formulated in this manner. Without being bound by any
interpretation, it is reasonable to expect that having a deficiency
of Li and excess of Mg allows one or the other octahedral site
cations, Mg or Fe, to occupy octahedral sites in the structure that
would normally be occupied by Li.
[0161] Based on the results obtained in this instance, where there
is an excess of the non-alkaline metal and a deficiency of the
alkali, it is believed that almost any metal added to the structure
of the parent compound such that substitution of the metal onto the
M1 crystallographic sites normally occupied by the main alkaline
metal occurs, would have the desired effect of improving the
electronic conductivity of the resulting compound.
[0162] Without being bound by any particular interpretation, we
note that LiFePO.sub.4 is found by first-principles calculations of
the spin-polarized type to have an unusual band structure of the
type known as a half-metal. The band gap is spin-sensitive and may
in one spin have a gap of about 1 eV while in the other being a
metal. It is also found that the electron effective mass is much
larger than the hole effective mass, which is consistent with
observation of higher electronic conductivity in a p-type
conductor.
[0163] Without being bound by any particular interpretation, it is
noted that a mechanism of defect formation can be understood from
the observations that the increased electronic conductivity of the
present materials is thermally activated and p-type, that there is
not a strict proportionality between dopant concentration and
conductivity, that similar increases in conductivity are possible
for dopants of 2+ through 6+ valence, that a two-phase reaction
exists upon delithiation, as shown in later Examples and as is seen
in undoped LiFeO.sub.4, and that a high capacity and high rate
capability are maintained over a wide range of lithiation of the
doped compounds. The olivine structure has continuous networks of
metal-filled anion polyhedra, including having the cations that
occupy the M2 sites (Fe site in LiFePO.sub.4) forming a
corner-sharing network of octahedra in the (010) plane, while the
cations on M1 (Li) sites form edge-sharing chains of octahedra in
the [100] direction. It is noted that the substitution of a cation
M that is supervalent to Li.sup.+ in the composition
Li.sub.1-xM.sub.xFePO.sub.4 is normally expected to result in donor
doping. In oxides, aliovalent solutes can be compensated by
electronic or ionic defects. The following point defect reactions
(in Kroger-Vink notation), illustrate these mechanisms for an
M.sup.3+ cation that is respectively compensated by electrons or by
cation vacancies on the M2 site:
1/2M.sub.2O.sub.3+FeO+1/2P.sub.2O.sub.5M.sub.Li.sup...+Fe.sub.Fe.sup.x+P.s-
ub.P.sup.x+4O.sub.O.sup.x+2e.sup.'30 1/2O.sub.2(g) (1)
1/2M.sub.2O.sub.3+1/2P.sub.2O.sub.5M.sub.Li.sup...+V.sub.Fe.sup."+P.sub.P.-
sup.x+4O.sub.o.sup.x (2)
[0164] In the first instance, electroneutrality is given by
[M.sub.Li.sup...]=n, namely the dopant acts directly as a donor
species. If the second mechanism is dominant, electroneutrality is
given by [M.sub.Li.sup...]=2[V.sub.Fe.sup."], in which case the
donor and vacancy charge-compensate one another and no direct
effect on the electronic carrier concentration is expected.
However, it can be shown that in this instance as well, secondary
defect equilibria should lead to an increase in the n-type
conductivity. Neither of these simple mechanisms can explain a
material of high p-type conductivity. An excess of acceptor point
defects above and beyond the dopant concentration, or a large
difference between hole and electron mobilities as discussed
earlier, are necessary. Possible acceptors in the LiFePO.sub.4
structure are cation vacancies (V.sub.Li.sup.', V.sub.Fe.sup."), or
oxygen interstitials (O.sub.i.sup."). The latter defect is unlikely
given the nearly hexagonal close-packed oxygen sublattice in
olivine, which should result in a high anion vacancy formation
energy.
[0165] A mechanism whereby cation doping on the Ml sites allows the
stabilization of solid solutions with a net cation deficiency, that
is, where the doped olivine endmember has a solid solution of
composition Li.sub.1-a-xM.sub.xFePO.sub.4 or
Li.sub.1-xM.sub.xFe.sub.1-bPO.sub.4, in which a and b are M1 or M2
vacancy concentrations respectively, is consistent with the
results. If the net charge due to a and b exceed that due to x,
then the material will have a net excess of acceptor defects
(Fe.sup.3+ ions). Taking for example an M.sup.3+ dopant, the
respective valences for a lithium deficient solid solution are
Li.sup.1+.sub.1-a-xM.sup.3+.sub.x(Fe.sup.2+.sub.1-a+2xFe.sup.+.sub.a-2x)(-
PO.sub.4).sub.3-. It is noted that lithium deficiency is
particularly likely under high temperature firing conditions due to
lithium volatility. The above defect mechanism is analogous to
allowing an extension of the solid solution field for the pure
Li-rich endmember phase to cation deficient solid solutions,
Li.sub.1-aFePO.sub.4. We recall that pure LiFePO.sub.4 has been
observed to decompose immediately to two co-existing phases upon
delithiation, LiFePO.sub.4 and FePO.sub.4, thereby pinning the Li
chemical potential and resulting in the flat intercalation voltage
vs. lithium concentration. Thus the insulating behavior of undoped
LiFePO.sub.4 throughout electrochemical cycling suggests negligible
mixed (Fe.sup.2+/Fe.sup.3+) iron valency in either phase. The
retention of either lithium or iron deficiency in the highly
lithiated solid solution can therefore result in charge
compensation by Fe.sup.3+ and p-type conductivity.
[0166] Regarding the delithiated FePO.sub.4 endmember phase, our
electrochemical data in later Examples indicate that it also
retains high electronic conductivity throughout cycling. The
influence of M1 site cation doping is expected to be quite
different for this phase. Starting with pure FePO.sub.4, in which
all iron is trivalent, cation doping will result in the formation
of divalent iron: M.sup.3+.sub.x(Fe.sup.2+.sub.3x-
Fe.sup.3+.sub.1-3x)PO.sub.4. This composition is obtained upon
delithiation of the solid solution given earlier. The dopant in
this instance may be viewed as an "interstitial" cation donor,
occupying normally unoccupied M1 sites, and n-type conductivity
should result. During operation as a lithium storage material, the
present materials may be a two-phase material, one phase p-type and
the other n-type, that change in their relative proportions as the
overall lithium concentration changes. A transition from p- to
n-type conductivity may be measurable for the two-phase material as
a whole as delithiation proceeds. This behavior may be observed
whether the cation dopant M occupies the M1 site, or preferentially
occupies the M2 site and displaces Fe to the M1 site.
[0167] The room temperature conductivity of some of the compounds
of the invention exceeds that of the well-established intercalation
cathodes LiCoO.sub.2 and LiMn.sub.2O.sub.4 in their lithiated
(discharged) states. At these high levels of electronic
conductivity, lithium ion transport is likely to limit the overall
rate of intercalation and deintercalation. That is, the effective
lithium chemical diffusion coefficient is likely to be limited by
lithium transport (i.e., the ionic transference number t.sub.Li is
.about.0). Because it is known that delithiation of LiFePO.sub.4
results in coexistence of two phases, lithium ingress and egress
from particles of the storage material requires growth in the
amount of one phase and a decrease in the amount of the other.
Without being bound by any particular interpretation of the
rate-limiting microscopic mechanism of phase transformation, it is
understood that a decrease in the crystallite size is beneficial to
ion transport. At the same time, it is necessary to simultaneously
accommodate electron flow to and from the particles. The structure
of the materials of the invention are almost ideal for providing
optimal mixed electronic-ionic transport in a battery system,
having a porous aggregate structure in which the nanoscale primary
crystallites can be surrounded by the electrolyte, allowing lithium
ion transport through a very small cross-sectional dimension, while
remaining electronically "wired" together through the sinter necks.
For materials in which electronic transport is limiting, it can
still be beneficial to decrease the crystallite size, as the
potential drop across particle is less for a material of higher
conductivity. (If ion transport is limiting, further increases in
the electronic conductivity are not expected to improve the rate
capability of a single particle significantly, but can improve the
electronic conductivity of a network of particles such as that
present in a typical composite electrode.)
[0168] Having a fine primary crystallite size due to doping as
provided by the present invention provides high rate capability.
Therefore, another feature of the materials of the present
invention is a structure characterized by primary crystallites
having at least a smallest dimension that is less than 200 nm,
preferably less than 100 nm, still preferably less than 50 nm, and
still more preferably less than 30 nm. According to the invention
the individual crystallites of the stated sizes are typically
joined by sintering, forming an interconnected but porous network.
In some cases, an average of at least 50% of the surface area of
the primary crystallites is exposed so that it can contact the
electrolyte. To determine the percentage of exposed surface area,
the following procedure can be used: the average primary particle
size and shape was measured, for instance by electron microscopy,
and the surface area per unit mass can be thus computed. This would
be the surface area that would result for completely isolated
particles. The specific surface area of the powder can then be
measured and compared to the first number. The latter should be at
least 50% of the former. In accordance with having a very small
primary crystallite size and aggregates that are not highly
densified, the specific surface areas of the materials of the
invention are preferably greater than about 10 m.sup.2/g, more
preferably greater than about 20 m.sup.2/g, more preferably greater
than about 30 m.sup.2/g, and still more preferably greater than
about 40 m.sup.2/g.
[0169] It is understood that olivines with other metals partially
or completely substituted for Fe, including but not limited to
LiMnPO.sub.4 and LiCoPO.sub.4, or others in the family of polyanion
compounds, including but not limited to those with continuously
joined networks of transition metal filled polyhedra within the
structure, may enjoy the benefits of improved electronic
conductivity, reduced crystallite size, high reversible charge
capacity, high rate capability, and other benefits described herein
when they are doped or processed according to the invention.
EXAMPLE 3
Electrode Fabrication and Electrochemical Tests
[0170] A composition Li.sub.0.998Nb.sub.0.002FePO.sub.4 was
prepared as described in examples 1 and 2 using lithium carbonate,
niobium phenoxide, iron oxalate, and ammonium dihydrogen phosphate,
and heat treated according to the procedure labeled as HT1 shown in
Table 2. The resulting powder was black and conductive, and was
cast as an electrode coating on an aluminum foil current collector,
using a standard formulation of 85 wt % of said composition, 10 wt
% SUPER P.TM. carbon, and 5 wt % PVDF binder. .gamma.-butyroactone
was used as the solvent. The positive electrode (cathode) coating
was tested against a lithium metal foil counterelectrode (anode) in
a standard cell assembly using CELGARD.RTM. 2400 separator film and
EC:DMC (+1M LiPF.sub.6) as the electrolyte. Galvanostatic tests
were performed at several current rates. FIG. 17A shows the first
electrochemical cycle at C/30 rate, in which it is seen that a
capacity of about 150 mA/g is obtained. A flat voltage plateau is
observed, indicating a two-phase equilibrium of constant lithium
chemical potential. FIG. 17B shows capacity vs. cycle number for
this electrode at a 1C rate (150 mA/g), to about 260 cycles. FIG.
17C shows that the coulombic efficiency vs. cycle number at 1C rate
(150 mA/g) is generally greater than about 0.997. These results
show that this material of the invention had good performance as a
storage cathode for rechargeable lithium battery systems, at
practical rates of charge and discharge, without requiring special
procedures, such as coating with conductive additives.
EXAMPLE 4
Electrode Fabrication and Electrochemical Tests of the Lithium
Storage Compounds and Electrodes of the Invention at High Discharge
Rates
[0171] The electrochemical performance of the undoped and doped
powders of Examples 1 and 2 were evaluated by using them in
electrodes of a variety of formulations and testing said electrodes
under a wide range of conditions as the positive electrode in a
liquid electrolyte cell, using lithium metal foil as the negative
electrode. Table 5 lists several of the electrode formulations that
were prepared and tested. All samples were tested using
CELGARD.RTM. 2400 or 2500 separator film and 1:1 EC:DEC with 1M
LiPF.sub.6 liquid electrolyte.
7TABLE 5 Lithium Storage Materials and Electrode Formulations
Active Active Materials Specific Electrode Material Composition and
Surface Formulation Loading Sample Heat Treatment Area (m.sup.2/g)
(wt percentages (mg/cm.sup.2) A LiFePO.sub.4, 700.degree. C./Ar 3.9
Cathode/Super- 5.3 P/Kynar 461 79/10/11 B LiFePO.sub.4, 700.degree.
C./Ar 3.9 Cathode/Super- 7.8 P/Kynar 461 79/10/11 C
(Li.sub.0.99Zr.sub.0.01)FePO.sub.4, .about.40 Cathode/Super-
>3.9 600.degree. C./Ar P/Alfa-Aesar PVdF 78.3/10.1/11.6 D
(Li.sub.0.99Zr.sub.0.01)FePO.sub.4, .about.40 Cathode/Super- 2.5
600.degree. C./Ar P/Alfa-Aesar PVdF 78.4/10.0/11.6 E
(Li.sub.0.99Zr.sub.0.01)FePO.sub.4, 41.8 Cathode/Super- 4.0
600.degree. C./Ar P/Kynar 2801 79/10/11 F
(Li.sub.0.99Zr.sub.0.01)FePO.sub.4, 41.8 Cathode/Super- 4.3 6000
C/Ar P/Kynar 2801 79/10/11 plasticized G
(Li.sub.0.99Zr.sub.0.01)FePO.sub.4, 41.8 Cathode/Super- 4.4
600.degree. C./Ar P/Kynar 2801 79/10/11 plasticized H
(Li.sub.0.99Zr.sub.0.01)FePO.sub.4, 26.4 Cathode/Super- 5.3
700.degree. C./Ar P/Kynar 461 79/10/11 I
(Li(Fe.sub.0.98Ti.sub.0.02)PO.sub.4, .about.40 Cathode/Super- 5.9
600.degree. C./Ar P/Kynar 461 79/10/11 J
(Li.sub.0.998Nb.sub.0.002)FePO.sub.4, .about.40 Cathode/Super- --
600.degree. C./Ar P/Alfa-Aesar PVdF 85/10/5
[0172] Table 5, Sample D.
[0173] A composition (Li.sub.0.99Zr.sub.0.01)FePO.sub.4, fired at
600.degree. C. in Ar according to the methods of Example 2, and
having a specific surface area of about 40 m.sup.2/g, was
formulated into an electrode by mixing 78.4 wt % of the active
material, 10.0 wt % of SUPER P.TM. carbon, and 11.6 wt % Alfa-Aesar
PVDF as the binder, using .gamma.-butyrolactone as solvent. The
mixing was done in a small plastic container containing one
Teflon.RTM.. ball using a dental amalgamator (Wig-L-Bug) for 5
minutes. Mixed suspensions were cast onto aluminum foil current
collectors, dried, and pressed at 4 tons/cm.sup.2. Electrochemical
test samples were cut from the pressed castings and assembled in
stainless steel test cells with lithium metal foil (Alfa Aesar,
Ward Hill, Mass., USA) as the counterelectrode and CELGARD.RTM.
2400 (Hoechst Celanese, Charlotte, N.C., USA) as the separator. The
liquid electrolyte used was 1:1 by wt ethylene carbonate and
diethyl carbonate with 1M LiPF.sub.6 added as the conductive
salt.
[0174] FIG. 18A shows the charge and discharge capacities of a cell
with about 2.5 mg/cm.sup.2 loading of the active material, observed
in continuous cycling at rates varying from 15 mA/g (C/10) to 3225
mA/g (21.5C) between the voltage limits of 2.8-4.2V, at room
temperature. It is noted that a stable capacity is obtained upon
cycling over a wide range of rates, to more than 150 cycles. FIG.
18B shows corresponding charge-discharge curves for the doped
sample, in which there is only a modest polarization, with a clear
voltage plateaus at .about.3.1V even at a discharge rate of 21.5C.
Comparing with published data for LiFePO.sub.4, it is clear that
the low doping levels used to increase conductivity and increase
specific surface area do not decrease the storage capacity at low
rates, but greatly increase the power density that is possible. The
low polarization is attributed to the high electronic conductivity
at the particle scale. Thus this electrode made using a compound of
the invention is seen to have high energy density at much higher
current rates than previously seen for undoped LiFePO.sub.4.
[0175] Table 5, Sample C.
[0176] An electrode prepared as described for Sample D of Table 5,
and having >3.9 mg/cm.sup.2 loading of active material, was
assembled in a Teflon.RTM. and stainless steel Swagelok.RTM. test
vessel with lithium metal foil (Alfa Aesar, Ward Hill, Mass., USA)
as the counterelectrode and CELGARD.RTM. 2400 (Hoechst Celanese,
Charlotte, N.C., USA) as separator. The liquid electrolyte used was
1:1 by wt ethylene carbonate and diethyl carbonate with 1M
LiPF.sub.6 added as the conductive salt.
[0177] FIG. 19A shows discharge capacities measured at 42.degree.
C. observed in continuous cycling tests. For the curve labeled
0.2C, the cell was charged and discharged at a current rate of 0.2C
(30 mA/g) between the voltage limits of 2-4.2V. For the other
curves, the cell was charged at a rate of 1.1 C (165 mA/g) and then
discharged at the rates shown. It is seen that this cell maintains
a significant discharge capacity and relatively little polarization
upon discharging at rates as high as 66.2C (9.93 A/g). Compared to
previously reported electrochemical test data for LiFePO.sub.4,
this cell can be discharged at a remarkably high power density
while still having significant energy density.
[0178] Table 5, Sample F, E, G, H.
[0179] Sample F was prepared from a composition
(Li.sub.0.99Zr.sub.0.01)Fe- PO.sub.4, fired at 600.degree. C. in Ar
according to the methods of Example 2, and having a specific
surface area of 41.8 m.sup.2/g. It was formulated into an electrode
by mixing 79 wt % of the active material, 10 wt % of SUPER P.TM.
carbon, and 11 wt % Kynar 2801 binder in .gamma.-butyrolactone as
solvent, using the procedures of Sample D and C. After casting and
drying, the coating was immersed in a plasticizing solvent of 15 wt
% propylene carbonate in methanol, then pressed and dried. The
resulting positive electrode (cathode) was tested against a lithium
metal foil counterelectrode (anode) in a Swagelok cell assembly
using CELGARD.RTM. 2500 separator film and 1:1 EC:DEC with 1M
LiPF.sub.6 liquid electrolyte.
[0180] FIG. 20 shows discharge curves for this cell measured by the
constant-current constant-voltage (CCCV) method whereby the cell
was first charged at 0.5C rate (75 mA/g), then held at the upper
limiting voltage of 3.8V until the charging current decayed to
0.001 mA, before discharging to 2V at the stated rate. Note that in
comparison to FIG. 19, the initial linear behavior upon discharge
is not seen, indicating that the linear region is a capacitive
response due to incomplete equilibration in the cell. (In later
calculations of the energy density of cell tested in continuous
cycling, the capacity of this linear region is not included.) The
results in FIG. 20 show quite remarkably that even at a 50C (7.5
A/g) discharge rate, about half of the capacity available at C/5
rate is provided by the cell.
[0181] FIG. 21 compares the discharge energy density of Sample F
with Samples E, G, and H from Table 5. All tests were conducted at
22-23.degree. C. Sample G was prepared in the same manner as Sample
F, and was tested by continuous cycling according to the procedure
of Sample C. Sample E was prepared and tested in the same manner as
Sample G, except that the electrode was not plasticized. Sample H
was prepared from a powder fired to a higher temperature than the
others in FIG. 21, 700C in Ar, and has a lower specific surface
area of 26.4 m.sup.2/g, and used Kynar 461 binder, but was
otherwise processed and tested in like manner. It is seen that all
four of the samples in FIG. 21 exhibit a remarkably high capacity
at high discharge C rates.
[0182] Table 5, Samples A and B
[0183] Samples A and B were prepared from undoped LiFePO.sub.4,
which after firing at 700C has a relatively low specific surface
area of 3.9 m.sup.2/g. The electrodes were prepared and tested in
like manner to Sample H in Table 5, and the results are shown in
FIG. 22, measured at 23, 31, and 42.degree. C. Unlike the results
in FIG. 21, however, the undoped samples show greatly inferior
discharge capacity that falls to about 20 mAh/g by about 5C (750
mA/g) rate. It is also seen in FIG. 22 that heating to a
temperature of 42.degree. C. does not significantly improve the
discharge capacity.
[0184] Comparison with Literature Data
[0185] Electrochemical test results have been reported for several
LiFePO.sub.4-based electrodes in the published literature. FIG. 23
compares the results from Sample F in Table 5 to results from
several published papers. It is seen that the electrodes of the
invention have markedly higher discharge capacity at high rates,
whereas the literature data typically shows a rapid decrease in
capacity with increasing rate at rates below 5C or 10C rate. This
comparison illustrates the novel high performance properties of the
lithium storage materials and electrodes of the current
invention.
[0186] Energy Density vs. Current Density
[0187] In FIGS. 24-27, we show the discharge energy density
available from the total mass of storage compound available in
several electrodes of Table 5, plotted against the current per gram
of storage material. The energy densities are obtained by
integrating the voltage vs. charge capacity curves. In FIG. 24,
results from Sample F are shown for a measurement temperature of
22.degree. C.; in FIG. 25, results for Sample G are shown for
measurement temperatures of 23, 31, and 42.degree. C.; in FIG. 26,
results for Sample I measured at 23.degree. C.; and in FIG. 27,
results are shown for Sample A for measurement temperatures of 23,
31, and 42.degree. C. Comparing FIGS. 24-26 with FIG. 27, the vast
improvement in the energy density of the lithium storage materials
of the invention compared to undoped LiFePO.sub.4 is clearly
seen
EXAMPLE 5
Storage Battery Cells
[0188] Example 4 illustrates the high discharge capacity available
from the lithium storage compounds of the invention, and electrodes
utilizing said compounds, at high discharge rates. Having shown
clearly the improved electrochemical properties of the lithium
storage compounds and electrodes of the invention, we now
illustrate storage battery cells of exceptional power density and
high energy density based on these compounds and electrodes.
[0189] It is well-known that typical lithium-ion batteries based on
laminated electrodes and designed for high energy density contain
25-35% by weight and 13-18% by volume of the positive electrode
storage compound, typically LiCoO.sub.2. While more detailed
calculations of the weight and volume fractions of materials are
used for specific designs, these approximate values provide an
adequate basis for determining the energy density and power density
of conventional cell designs utilizing the present lithium storage
compounds. Accounting for the 29% lower crystal density of
LiFePO.sub.4 compared to LiCoO.sub.2, and assuming a somewhat lower
packing density due to the high specific surface area, it is
conservatively estimated that an optimized cell could contain 10-20
wt % of the positive electrode active material. Using the results
of Example 4 for electrodes tested against lithium metal negative
electrodes, and taking into account its slightly lower cell voltage
when used in conjunction with a carbon electrode (3.25 vs. 3.7 V),
the power density--energy density results shown in FIG. 28 are
obtained. Results are shown for 10 wt %, 15 wt %, and 20 wt % of
the positive electrode active material. Power and energy densities
for complete discharge of a cell of 800-1500 W/kg and 30-60 Wh/kg
at a 20C (3 A/g) rate, 1500-4200 W/kg and 15-30 Wh/kg at a 50C (7.5
A/g) rate, and 2500-5000 W/kg and 5-10 Wh/kg at a 80C (12 A/g)
rate, are obtained. Such cells could provide power densities not
possible in current nickel metal-hydride (400-1200 W/kg, 40-80
Wh/kg) and lithium-ion battery technology (800-2000 W/kg, 80-170
Wh/kg). These capabilities, in a low-cost and ultra-safe storage
material, may be especially attractive for high power and large
battery applications including but not limited to power tools and
hybrid and electric vehicles.
EXAMPLE 6
Doping From Milling Media and Containers
[0190] This example shows that doping to yield high electronic
conductivity can be accomplished by using suitable milling media
and containers. It also shows that the high electronic conductivity
of the materials of the invention is obtained without excessive
carbon or other conductive additives. Table 6 shows the results of
carbon and zirconium analysis of several materials prepared
according to the methods of Examples 1 and 2. It is seen that
milling with 3/8" ZrO.sub.2 milling media can add a detectable
concentration of Zr to the samples. Amongst the nominally undoped
samples, a high conductivity of about 10.sup.-3 S/cm is observed
when the Zr concentration from the milling media is 0.018. Taking
this added Zr into account, the composition of the sample is of
type Li.sub.1-zZr.sub.aFePO.sub.4, similar to other high
conductivity samples. It is also seen that the polypropylene
milling jar has added some excess carbon to this sample. When 1/4"
ZrO.sub.2 milling media are used, negligible Zr doping occurs. An
undoped sample fired at 800C has 0.25 wt % carbon, and a low
conductivity of 10.sup.-8 S/cm.
[0191] Lightly doped samples such as in Table 1 that have been
milled with zirconia milling media can thus also be doped with Zr
in addition, improving the conductivity.
[0192] The four Zr and Nb doped samples, were formulated to have
Li.sub.1-aM".sub.aFePO.sub.4 composition and have high electronic
conductivity. The concentration of carbon is less than 2 weight
percent in one instance, and less than 1 weight percent in the
other three instances. The sample of highest conductivity,
10.sup.-2 S/cm, has the lowest carbon concentration, only 0.32
weight percent, nearly the same as the highly insulating undoped
samples. The sample with the highest carbon concentration has the
lowest conductivity. These results show that the high electronic
conductivity of doped samples is not correlated with carbon
concentration but instead with doping as described herein.
8TABLE 6 Carbon analysis of conductive lithium iron phosphate
materials. Carbon Zr Conductivity Composition Preparation Method
(wt %) (wt %) 2-probe (S/cm) Undoped (large batch) Polypropylene
bottle, 0.25 0.009 10.sup.-10 700.degree. C. 3/8" ZrO.sub.2 media
Undoped (Li.sub.0.99FePO.sub.4) Polypropylene bottle, 2.41 0.018
(.about.10.sup.-3) 700.degree. C. 3/8" ZrO.sub.2 media Undoped
Porcelain jar, 0.25 10.sup.-8 800.degree. C. 1/4" ZrO.sub.2 media
1% Zr doped Porcelain jar, 1.46 10.sup.-4 700.degree. C. 1/4"
ZrO.sub.2 balls 1% Zr doped Porcelain jar, 0.86 10.sup.-3
800.degree. C. 1/4" ZrO.sub.2 balls 1% Nb doped Porcelain jar, 0.56
10.sup.-3 800.degree. C. Tiny ZrO.sub.2 balls 1% Nb doped
Polypropylene bottle, 0.32 10.sup.-2 800.degree. C. 3/8" ZrO.sub.2
media
EXAMPLE 7
Compositions With Dopant Not in Solid Solution
[0193] In this example, as in Example 1, it is shown that when a
doped composition similar to the preceding examples of high
electronic conductivity is prepared, but the dopant is not in solid
solution, then the composition is not conductive. In Example 2, it
was shown that a composition Li.sub.0.99Nb.sub.0.01)FePO.sub.4 has
markedly improved conductivity and electrochemical storage
properties compared to an undoped LiFePO.sub.4 when the Nb dopant
is in solid solution in the crystal lattice. Here it is shown that
the same composition prepared with the dopant not in solid
solution, but precipitated as a secondary phase, is substantially
insulating.
[0194] 1 mole % Nb-doped LiFePO.sub.4 was prepared using iron
acetate, Fe(CH.sub.3COO).sub.2 as the Fe precursor. Niobium
phenoxide, Nb(C.sub.6H.sub.5O).sub.5 was used as the source of the
dopant. The theoretical content of Fe in iron acetate is 32.12 wt
%. However, the iron content of iron acetate frequently deviates
from the ideal value. Thus it was expected that the composition of
the compound would deviate from a nominal composition
(Li.sub.0.99Nb.sub.0.01)FePO.sub.4 that provides good electronic
conductivity. A batch of powder was formulated according to the
following proportions of starting materials:
9 1 mole % Nb-doped LiFePO.sub.4 .about.4 g batch
NH.sub.4H.sub.2PO.sub.4 2.3006 g (99.998%, Alfa-Aesar)
Li.sub.2CO.sub.3 0.7316 g (99.999%, Alfa-Aesar)
Fe(CH.sub.3COO).sub.2 3.7867 g (99.9%, Alfa-Aesar)
Nb(C.sub.6H.sub.5O).sub.5 0.1116 g (Alfa-Aesar)
[0195] Each of the components was weighed in an argon-filled glove
box. They were then removed from the glove box and ball milled,
using zirconia milling balls (.about.1/4" diameter, 400-450 g total
weight) in a porcelain milling jar (300 ml capacity) for 24 hours
in acetone (150-160 ml) at 230 rpm. The milled mixture was dried at
a temperature not exceeding 80.degree. C., and then ground with a
mortar and pestle in the argon-filled glove box. The mixture was
then heat treated in two steps. A first heat treatment at
350.degree. C. for 10 hours was conducted in a flowing Ar (99.999%
purity) atmosphere (>400 cc/min). The powder sample was then
ground in laboratory air atmosphere, using a mortar and pestle, and
subjected to a second heat treatment at a higher temperature
(600.degree. C. to 700.degree. C.) for 20 hours, in flowing Ar gas
(>400 cc/min). The heating and cooling rates for each step were
5.degree. C./min. Before heating, purging of the furnace tube in
flowing Ar for about 1 hour was conducted.
[0196] In contrast to the cases where iron oxalate
(FeC.sub.2O.sub.4.2H.su- b.2O) is used as the starting materials, a
2-probe resistance measurement of this sample showed that the
conductivity is less than 10.sup.-7 S/cm at a temperature of
23-27.degree. C. X-ray diffraction of a sample fired at 600C for 20
h in Ar showed that it was predominantly LiFePO4 but had a small
amount of an unidentified secondary phase. TEM analysis showed that
the dopant Nb was not detectable inside the particles, but was
segregated as a secondary phase. Furthermore, the specific surface
area of this material was much lower than it is in samples prepared
so that the Nb dopant is in solid solution, being 14.3 m.sup.2/g
for 600C firing. Thus it is shown that in this material, when a
substantial amount of the added Nb dopant is not in solid solution
in the crystalline particles, an increased conductivity is not
observed, nor is the advantageous feature of metal additives of
diminishing the crystallite size realized. It is understood that
the iron acetate precursor, being a suitable reactant for the
formation of LiFePO.sub.4, is suitable for producing highly
conductive compositions when the overall composition is known and
more precisely controlled.
EXAMPLE 8
Solid State Reaction Synthesis of LiFePO.sub.4
[0197] This example describes the preparation of LiFePO.sub.4,
using wustite iron oxide, FeO, and lithium metaphosphate,
LiPO.sub.3, as precursors. An advantage of these precursors is that
they form a closed or nearly closed reaction system, by which it is
meant that upon heat treatment, few if any gaseous species are
produced as a reaction by product. Adjustments to the relative
amounts of the reactants, and the addition of other constituents
such as the dopants in the form of oxides can be used in order to
obtain compositions comprising the materials of the invention.
[0198] A batch of 6 g LiFePO.sub.4 was prepared by using starting
materials of the following amounts: 2.733 g FeO (99.5%, Alfa-Aesar,
Ward Hill, Mass., USA) and 3.267 g LiPO.sub.3 (97%, City Chemical
LLC., West Haven, Conn., USA). The components were weighed in an
Ar-filled glove box, and transferred to a porcelain jar and
ball-milled in acetone for 48 h using zirconia milling balls. The
acetone was evaporated from the milled powder at a low temperature
(<100.degree. C.), and the dried powder was ground with a mortar
and pestle and pressed into pellets. The pellets were embedded in
loose powder of the same material and placed in alumina crucibles
and subjected to a single heat treatment under Ar atmosphere at
550-900.degree. C. for 20 h.
[0199] The heat-treated samples were light to medium grey in color.
Predominantly single-phase LiFePO.sub.4 was obtained for all
heat-treatment temperatures, as identified by X-ray diffraction.
Minor amounts of Fe.sub.2P and Fe phases were detected by XRD at
heat-treatment temperatures at and above 600.degree. C.
EXAMPLE 9
Solid State Reaction Synthesis of Nb-doped LiFePO.sub.4
[0200] Conductive compositions of the invention are obtained using
the starting materials and basic procedure of Example 8, and by
adding dopants in the form of oxides, hydroxides or alkoxides to
obtain the dopant metal ion in the preferred valence state. A
conductive sample with the nominal formulation LiFePO.sub.4+1 mole
% Nb was prepared using the precursors of Example 8 and adding a
small amount of the dopant niobium phenoxide,
Nb(C.sub.6H.sub.5O).sub.5. A batch of about 1 g powder was prepared
by using 0.4530 g FeO, 0.5416 g LiPO.sub.3 and 0.0352 g
Nb(C.sub.6H.sub.5O).sub.5 (99.99%, Alfa-Aesar, Ward Hill, Mass.,
USA). The powders were milled, as described in Example 6, and then
pressed into pellets and heat-treated under Ar atmosphere at
600.degree. C. for 20 h. Some sintered pellets were also annealed
at 850.degree. C. to obtain more densified samples or samples with
more coarsened crystallites.
[0201] In contrast to the undoped powder of Example 8, the
resulting powder was dark grey in color, which gave an indication
of increased electronic conductivity, compared to the undoped
sample. X-ray diffraction analysis showed predominantly a single
crystalline phase of the triphylite LiFePO.sub.4 structure.
Resistance measurements were made using a two-contact method with
metal probes located about 5 mm apart on the fired pellets, and
showed a resistivity of about 150 k.OMEGA., in contrast to the
insulating sample of Example 8, which when made by the same
procedure and from the same starting materials except for the
absence of doping with niobium phenoxide showed a resistance of
>200 mega ohms (M.OMEGA.). Thus it is shown that the doped
compositions of the invention prepared according to the methods of
this example provide an increased electronic conductivity compared
to an undoped composition.
EXAMPLE 10
Solid State Reaction Synthesis of Conductive LiFePO.sub.4
[0202] In this example, doped LiFePO.sub.4 with increased
electronic conductivity is prepared using the starting materials
and methods of Example 8 and 9, except that the conductive
compositions of the invention are obtained by adding dopants in the
form of oxides wherein the dopant are in the preferred final
valence state, including but not limited to TiO.sub.2,
Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, ZrO.sub.2, Al.sub.2O.sub.3, MgO,
or WO.sub.6. The dopant oxide is added to the starting mixture of
reactants in a quantity sufficient to give a desired concentration
in the final product. Using the mixing and firing procedures of
Examples 8 and 9, conductive compositions of the invention are
obtained.
EXAMPLE 11
Solid-state Reaction Synthesis
[0203] This example describes the all-solid state reaction
synthesis of LiFePO.sub.4 or conductive doped LiFePO.sub.4, using
wustite iron oxide, FeO, lithium oxide, Li.sub.2O, and
phosphorous(V) oxide, P.sub.2O.sub.5, as precursors to the major
metallic constituents and metal alkoxides and metal oxides as the
source of the dopants. This set of precursors also forms a closed
or nearly closed reaction system, from which few if any gaseous
species are evolved during synthesis.
[0204] A batch of 12 g LiFePO.sub.4 was prepared by using starting
materials of the following amounts: 5.463 g FeO (99.5%, Alfa-Aesar,
Ward Hill, Mass., USA), 1.136 g Li.sub.2O (99.5%, Alfa-Aesar, Ward
Hill, Mass., USA) and 5.398 g P.sub.2O.sub.5 (99.99%, Alfa-Aesar,
Ward Hill, Mass., USA). The components were weighed in an Ar-filled
glove box, transferred to a polypropylene jar and ball-milled for
48 h using zirconia milling balls. Special precautions were taken
to avoid any exposure of the reactant mixture to air, due to the
very hygroscopic nature of P.sub.2O.sub.5. For instance, a liquid
milling medium (e.g. acetone) was not added prior to milling. The
dry, milled powder was extracted from the milling jar in the glove
box, ground with mortar and pestle and pressed into pellets. The
pellets were placed in alumina crucibles and subjected to a single
heat treatment at 550.degree. C. or 850.degree. C. for 20 h., after
which the samples were found by X-ray diffraction to contain
LiFePO.sub.4 as the major crystalline phase. Doped samples are
prepared in the same manner, except with the addition of a dopant
salt such as a metal alkoxide or metal oxide prior to the mixing
and milling steps.
EXAMPLE 12
Solid-state Reaction Synthesis
[0205] This example describes the preparation of undoped or doped
LiFePO.sub.4, using iron oxalate, FeC.sub.2O.sub.4.2H.sub.2O, and
lithium metaphosphate, LiPO.sub.3, as precursors. Gaseous species
formed during synthesis are limited to one formula unit carbon
dioxide CO.sub.2, one formula unit carbon monoxide CO and two
formula units water H.sub.2O per formula unit reacted
FeC.sub.2O.sub.4.2H.sub.2O.
[0206] A batch of 1 g LiFePO.sub.4 was prepared by using starting
materials of the following amounts: 1.134 g
FeC.sub.2O.sub.4.2H.sub.2O (99.99%, Aldrich, Milwaukee, Wis., USA)
and 0.5410 g LiPO.sub.3 (97%, City Chemical LLC., West Haven,
Conn., USA). The components were weighed in an Ar-filled glove box,
and ball milled in acetone in a porcelain jar for about 24 h, using
zirconia milling balls. The acetone was evaporated from the milled
powder at a low temperature (<100.degree. C.), and the dried
powder was ground using a mortar and pestle. The milled powder was
heat treated at 350.degree. C. for 10 h under flowing Ar gas. The
heat-treated powder samples were then ground again with a mortar
and pestle and pressed into pellets before a second heat-treatment
step. The pellets were placed in alumina crucibles and heated to
600.degree. C. or 700.degree. C. for 20 h under Ar gas. X-ray
diffraction showed that a predominantly single-phase LiFePO.sub.4
was obtained for both heat-treatment temperatures. A minor amount
of another detectable phase (2.theta..about.27, 28, 30 and
31.degree.) was also observed. Doped samples are prepared in the
same manner, except with the addition of a dopant salt prior to
mixing and milling.
EXAMPLE 13
Solid-state Reaction Synthesis
[0207] This example describes the preparation of undoped or doped
LiFePO.sub.4, using iron oxalate, FeC.sub.2O.sub.4.2H.sub.2O,
lithium oxide, Li.sub.2O, and phosphorous(V) oxide, P.sub.2O.sub.5,
as precursors. The formation of gaseous species during synthesis is
limited to one formula unit carbon dioxide CO.sub.2, one formula
unit carbon monoxide CO and two formula units water H.sub.2O per
formula unit reacted FeC.sub.2O.sub.4.2H.sub.2O.
[0208] A batch of 1 g LiFePO.sub.4 was prepared by using starting
materials of the following amounts: 1.134 g
FeC.sub.2O.sub.4.2H.sub.2O (99.99%, Aldrich, Milwaukee, Wis., USA),
0.09421 g Li.sub.2O (99.5%, Alfa-Aesar, Ward Hill, Mass., USA) and
0.4475 g P.sub.2O.sub.5 (99.99%, Alfa-Aesar, Ward Hill, Mass.,
USA). The components were weighed in an Ar-filled glove box, and
dry-milled in a porcelain jar for about 24 h using zirconia milling
balls. The milled powder was extracted from the milling jar in the
glove box and ground using a mortar and pestle. The powder was then
heat treated at 300.degree. C. for 10 h under flowing Ar gas,
ground again and pressed into pellets before a second heat
treatment step. The pellets were placed in alumina crucibles and
heated to 600.degree. C. or 700.degree. C. for 20 h under Ar gas.
X-ray diffraction showed a predominantly single-phase LiFePO.sub.4
for both heat-treatment temperatures. A minor amount of another
detectable phase (2.theta..about.27 and 28.degree.) and possibly a
minor amount of Fe.sub.3O.sub.4 was also observed. Doped samples
are prepared in the same manner, except with the addition of a
dopant salt prior to mixing and milling.
EXAMPLE 14
Chemically Delithiated Doped Conductive LiFePO.sub.4
[0209] This example describes the chemical delithiation of a doped
and conductive LiFePO.sub.4, after which it remains highly
electronically conductive as predominantly an FePO.sub.4 phase. The
chemical reduction of LiFePO.sub.4 was conducted by the addition of
a strong reducing agent, in this case nitronium
hexafluorophosphate, NO.sub.2PF.sub.6, to a suspension of the
starting material and acetonitrile, CH.sub.3CN. Nitrogen dioxide
gas, NO.sub.2, and solvated lithium hexafluorophosphate,
LiPF.sub.6, is formed during the reaction together with the reduced
FePO.sub.4, according to:
LiFePO.sub.4(s)+NO.sub.2PF.sub.6(sol.)
.fwdarw.NO.sub.2(g)+LiPF.sub.6(sol.-
)+FePO.sub.4(s)(sol.=solvated)
[0210] Specifically a powder of (Li.sub.0.99Nb.sub.0.01) FePO.sub.4
was delithiated. To obtain a relatively complete level of
delithiation, the molar ratio NO.sub.2PF.sub.6:
(Li.sub.0.99Nb.sub.0.01) FePO.sub.4 was set to 2:1. For a batch of
0.6 g (Li.sub.0.99Nb.sub.0.01) FePO.sub.4 (prepared according to
Example 2), an amount of 1.453 g of NO.sub.2PF.sub.6 (98%, Matrix
Scientific, Columbia, S.C., USA) was used. Both reactants were
weighed in an Ar-filled glove box and transferred to a filtering
flask equipped with a rubber stopper. A thin glass tube was fitted
through a hole in the rubber stopper and a silicone tube was fitted
to the tubulation opening on the flask side. 100 ml of acetonitrile
(99.998%, anhydrous, Alfa-Aesar, Ward Hill, Mass., USA) was added
to the beaker, and the glass tube was adjusted so that the tip was
positioned under the liquid surface. The resulting concentration of
NO.sub.2PF.sub.6 in the solution was ca. 0.08 M. A flow of Ar gas
was introduced at the glass tube end, so that the gaseous species
formed during the reaction were led away through the silicone tube
to an exhaust hood. The reaction was allowed to proceed for 24 h,
while stirring with a magnetic stirrer. The resulting powder was
separated from the solution by filtering through a Buichner funnel
equipped with filter paper (#595, Schleicher & Schuell). The
powder was thoroughly rinsed in pure acetonitrile and dried under
vacuum for two hours. The remaining powder was analysed by X-ray
diffraction and showed a single-phase orthorhombic FePO.sub.4
structure. The powder was black in color, and when pressed into a
pellet, was highly conductive. Thus this example shows that the
compounds of the invention remain highly electronically conductive
upon delithiation, and that a partially delithiated compound
comprises two phases, one relatively highly delithiated and the
other relatively delithiated, both of which are electronically
conductive.
[0211] Those skilled in the art would readily appreciate that all
parameters and configurations described herein are meant to be
exemplary and that actual parameters and configurations will depend
upon the specific application for which the systems and methods of
the present invention are used. Those skilled in the art will
recognize, or be able to ascertain using no more than routine
experimentation, many equivalents to the specific embodiments of
the invention described herein. It is, therefore, to be understood
that the foregoing embodiments are presented by way of example only
and that, within the scope of the appended claims and equivalents
thereto, the invention may be practiced otherwise than as
specifically described. Accordingly, those skilled in the art would
recognize that the use of an electrochemical device in the examples
should not be limited as such. The present invention is directed to
each individual feature, system, or method described herein. In
addition, any combination of two or more such features, systems or
methods, if such features, systems or methods are not mutually
inconsistent, is included within the scope of the present
invention.
* * * * *